Rolling mill equipped with on-line roll grinding system and grinding wheel

ABSTRACT

A grinding head unit is constituted by a grinding wheel, a drive device for rotating the grinding wheel, and a movement device for moving the grinding wheel. When vibration of a mill roll is applied to the grinding wheel, a plain wheel integral with an abrasive layer of the grinding wheel and having an elastically deforming function is deflected to absorb the vibration energy. The contact force between the abrasive layer and the mill roll is measured for determining a profile of the mill roll. The mill roll can be thereby ground into a target profile while absorbing the vibration transmitted from the mill roll and measuring the profile of the mill roll, without causing any chattering marks.

This application is a divisional of application Ser. No. 08/590,672,filed Jan. 24, 1996 now U.S. Pat. No. 5,954,565 which was a divisionalof application Ser. No. 08/070,760 filed Jun. 3, 1993, now U.S. Pat. No.5,562,525.

BACKGROUND OF THE INVENTION

The present invention relates to a rolling mill equipped with an on-lineroll grinding system, and more particularly to an on-line roll grindingsystem for effectively grinding mill rolls on-line without undergoinginfluences of vibration of work rolls.

Generally, when slabs are rolled by work rolls of a strip rolling mill,there occurs a periphery difference between the rolling zone and theunrolling zone because only the former is abraded or worn away. Thisimposes such restrictions upon the rolling operation as necessity ofrolling slabs in order of wide ones to narrow ones. To solve, thatproblem, there have been proposed various techniques and control methodsin relation to on-line roll grinders.

For example, “Development of On-Line Roll Grinders”, Mitsubishi Giho,Vol. 25, No. 4, 1988, discloses a technique that a plurality of cupgrinding stones are arranged along one work roll and mounted to aone-piece frame, the frame being always moved in its entirety over acertain range, and the cup grinding stones are not positively driven torotate but passively driven with the aid of torque of the work roll,thereby grinding the entire surface of the work roll (hereinafterreferred to as first prior art).

Also, JP, U, 58-28705 discloses a technique that one roll grinding unitis disposed for one work roll, contact rolls serving as position sensorsare held in contact with neck portions at both ends of the work roll onthe side thereof opposite to the roll grinding unit, the positionsensors detecting an offset of the work roll, and a shifting device iscontrolled to move a grinding wheel following the detected offset(hereinafter referred to as second prior art).

Further, “On-Line Constant Pressure Grinding for Work Rolls”,Proceedings of 1992 Spring Lecture Meeting of Precision EngineeringSociety of Japan, reports an experimental result of forming an abrasivelayer of a cup grinding stone using abrasives of cubic boron nitride(CBN), arranging a spindle of the grinding stone perpendicularly to theaxis of a work roll, and grinding the work roll (hereinafter referred toas third prior art).

In addition, JP, U, 58-28706 and JP, U, 62-95867 disclose a techniquethat a cup grinding stone arranged substantially perpendicular to a workroll is mounted to a spindle slidably in its axial direction, and thegrinding stone is axially supported at its backside by an elastic bodydirectly or via a boss, thereby absorbing vibration of the work roll(hereinafter referred to as fourth prior art).

Meanwhile, in strip rolling machines, it has been conventionallyproposed to measure the profile of a work roll and control the crown andshape of a strip by utilizing the measured profile. As a technique formeasuring the profile of the work roll, an on-line roll profile meterhas been developed which employs a ultrasonic profile meter. The systemconfiguration of this profile meter is described in “Development ofOn-Line Roll Grinding System with Profile Meter”, Mitsubishi Giho, Vol.29, No. 1, 1992. In this system, a column of water is produced between aprobe with a ultrasonic profile meter built therein and a work roll, andthe spacing from the probe to the work roll is determined based on thetime required for pulsatory ultrasonic waves emitted from the probe toreciprocate between the probe and the surface of the work roll(hereinafter referred to as fifth prior art).

SUMMARY OF THE INVENTION

Work rolls of a rolling mill are each held by bearings assembled inmetal chocks and rotated at a high speed. The metal chocks each havegaps in its inner and outer circumferences for facilitating replacementof the work roll and the bearing. During rotation, therefore, the workroll is rotated while moving back and forth in the gaps. In addition,since a cylindrical portion of the work roll undergoes an offset withrespect to the bearings, the work roll is vertically moved by ascrewdown device during strip rolling. As a result of those movementscombined with each other, the work roll is rotated while vibrating atall times.

Generally, when grinding cylindrical works, the work to be ground issupported by a tail stock rotating With high precision to carry out thegrinding under a condition that vibration of the work is suppressed tobe as small as practicable. In an attempt to grind the work roll whilerolling a strip in the rolling mill, however, it is impossible to carryout the grinding under a condition of very small vibration like works inthe above ordinary case. During the rolling, the work roll is rotatedwhile vibrating usually with an amplitude of 20 μm to 60 μm and anacceleration of 1 G to 2 G. An on-line roll grinding system mustprecisely grind the work roll under such a condition.

With the above first to third prior arts, when whey are applied to thegrinding of such a vibrating work rols, there produce irregularities onthe surface of the work roll due to chattering marks. Also, the grindingstone or wheel is remarkably worn away with the impact force caused bychattering, and its service life is so shortened as to require morefrequent replacement. Further, it is difficult to control the contactforce in the case of grinding the work roll into a predeterminedprofile.

The above fourth prior art is designed to absorb the vibration of thework roll by the elastic body. With this prior art, however, since theentire grinding stone including a stone base is supported by the elasticbody and moved back and forth, there accompanies a problem that themovable mass of the grinding stone, i.e., the weight of a portion whichis forced to move following the vibration, is great. Even in the case ofusing, as the abrasive layer of the grinding stone, abrasives of cubicboron nitride (CBN) which has a high grinding ratio, the movable mass ofthe grinding stone supported by the elastic body and moving back andforth is at least more than 5 Kg, including the stone itself of whichdiameter is assumed to be 250 mm, slide bearings and sealing parts.Supposino that an allowable value of change in the contact force betweenthe work roll and the grinding stone is 4 Kgf and the amplitude ofvibration of the work roll is 30 μm, the spring constant of the elasticbody must be set to 130 Kgf/mm. Under the above conditions, the naturalfrequency of the movable portion including the elastic body iscalculated to be 80 c/s. The movable portion including the elastic body,which has such a low natural frequency, is caused to resonate with thevibration of the work roll, hereby producing chattering marks on theroll surface and accelerating abrasion of the grinding stone. If thestone size is reduced to make the movable mass smaller, the grindingability would be lowered to a large extent.

The cup grinding stone is slidabe in the axial direction of the spindleand supported at its backside by the elastic body. Durung the rollgrinding, however, a coolant, grinding dust and the like are scatteredaround the grinding stone, and these foreign mat ers may enterclearances between the grinding stone and the spindle to impede smoothmovement of the grinding stone. It is therefore difficult for theelastic body to stably develop its function for a long period of time.

The above first and second prior arts also have the following problem.The unrolling zone of the work roll is not subjected to abrasion by thestrip and hence should be ground to a larger extent than the rollingzone. With the above first embodiment, however, because thecircumferential speed of the cup grinding stone is limited by therotational speed of the work roll, the grinding rate can be controlledonly by changing the contact force in the case of grinding the unrollingzone to a larger extent. This imposes a limitation upon the grindingrate, making it difficult to keep a constant roll profile for a longperiod of time.

With the above second embodiment, since the spindle is arrangedperpendicularly to the work roll, the abrasive layer of the grindingwheel contacts the work roll at two right and left points of its annularabrasives surface and the work roll is simultaneously ground at thosetwo points. Therefore, if the work roll has a periphery difference, thetwo grinding surfaces interfere with each other to case chatteringmarks. Also, the contact at two points between the grinding wheel andthe work roll leads to a difficulty in controlling the contact forcethere between. Additionally, the position sensors have a problem ofreliability under severe environment of rolling machines. From thesereasons, the above second embodiment has not yet been put into practice.

Measurement of a roll profile will now be considered. After a strip isrolled by work rolls, the work rolls are each worn away about 2μm/radius per coil of a hot rolling steel strip, for example, in thezone where the strip is rolled. Due to this wear and the thermal crownresulted from an increase in the roll diameter caused by the heat of thestrip, the profile of the roll surface is changed over the entire lengthof a roll barrel. If the roll profile can be correctly measured, theon-line roll grinder provided in the rolling mill can grind the workroll into the roll profile optimum for the rolling. Heretofore, it hasbeen regarded to be difficult to correctly measure the roll profile ofthe work roll, which is vibrating and sprayed with a large amount ofroll coolant at all times, in the rolling mill, i.e., on-line.

As known from the above fifth prior art, there has been developed anon-line profile meter of the type that a column of water is producedbetween a probe and a work roll for determining the spacing from theprobe to the work roll based on the time required for ultrasonic wavesto reciprocate between the probe and the surface of the work roll.However, because of measuring the time during which ultrasonic wavesreciprocate through the very short distance, the measure time is alsovery short and the profile distance is on the order of microns. There ishence a fear that even a small error of the measured time may result ina large profile error. Particularly, in the case of using the ultrsonicprofile meter for a long period of time, even if the state of the columnof water between the probe and the roll is so changed as to cause anerror in the measurement, it is difficult to find such an error.Although the ultrasonic profile meter can always correctly measure theroll profile in principles, there is a difficulty in maintaining highprecision at all times in practice when the ultrasonic profile meter isused for a long period of time under the severe environment as mentionedabove. The presence of plural measuring probes also makes it difficultto perform compensation.

A first object of the present invention is to provide a rolling millequipped with an on-line roll grinding system and a grinding wheel forthe on-line roll grinding system in which vibration from a work roll isabsorbed to enable precise grinding with good roughness of the rollsurface without giving rise to any chattering marks.

A second object of the present invention is to provide a rolling millequipped with an on-line roll grinding system and a grinding wheel forthe on-line roll grinding system in which the profile of a work roll canbe correctly measured by a roll profile meter provided integrally withthe on-line roll grinding system.

To achieve the above first object, in accordance with the presentinvention, there is provided a rolling mill equipped with an on-lineroll grinding system comprising a plain type grinding wheel positionedto face one of a pair of mill rolls for grinding one said mill roll,grinding wheel drive means for rotating said grinding wheel through aspindle, grinding wheel movement means for pressing said grinding wheelagainst said mill roll, and grinding wheel traverse means for movingsaid grinding wheel in the axial direction of said mill roll, whereinsaid grinding wheel comprises a plain wheel attached to said spindle andan abrasive layer fixed to one side of said plain wheel, said plainwheel having an elastically deforming function to absorb vibrationtransmitted from said mill roll.

In the above on-line roll grinding system, preferably, said grindingwheel is arranged such that a contact line between said abrasive layerand said mill roll is defined only in one side as viewed from the centerof said grinding wheel, and more preferably, said grinding wheel isarranged with said spindle inclined by a small angle relative to thedirection perpendicular to an axis of said mill roll, so that a contactline between said abrasive layer and said mill roll is defined only inone side in the roll axial direction as viewed from the center of saidgrinding wheel.

Preferably, said abrasive layer is annular in shape, and said abrasivelayer contains super abrasives, i.e., cubic boron nitride abrasivesand/or diamond abrasives.

Also, said plain wheel preferably has a spring constant of 1000 Kgf/mmto 30 Kgf/mm, and more preferably a spring constant of 500 Kgf/mm to 50Kgf/mm.

Preferably, said abrasive layer contains cubic boron nitride abrasives,said abrasives having a concentration of 50 to 100 and a grain size of80 to 180, and a resin bond is used as a binder for said abrasives.

Preferably, said on-line roll grinding system further comprises loaddetecting means for measuring the contact force between said grindingwheel and said mill roll, and control means for controlling saidgrinding wheel movement means to optionally change the contact forcemeasured by said load detecting means so that a grinding rate of saidgrinding wheel on said mill roll is changed, for thereby grinding saidmill roll into a predetermined roll profile.

Said on-line roll grinding system may further comprise load detectingmeans for measuring the contact force between said grinding wheel andsaid mill roll, and control means for controlling said grinding wheelmovement means so that the contact force measured by said load detectingmeans is held constant, and for simultaneously controlling said grindingwheel traverse means to optionally change a traverse speed of saidgrinding wheel in the roll axial direction so that a grinding rate ofsaid grinding wheel on said mill roll is changed, for thereby grindingsaid mill roll into a predetermined roll profile.

Preferably, said grinding wheel movement means comprises a rotationdrive source, and a ball screw mechanism or a gear mechanism having asmall backlash and converting rotation of said rotation drive sourceinto axial movement of said grinding wheel movement means for movingsaid grinding wheel back and forth relative to said mill roll.

Preferably, said on-line roll grinding system comprises at least twogrinding head units for each of said mill rolls, each of said twogrinding head units including said grinding wheel, said grinding wheeldrive means, said grinding wheel movement means and said grinding wheeltraverse means, whereby said two grinding head units can grind said millroll independently of each other.

In this case, said on-line roll grinding system preferably furthercomprises control means for stopping said grinding wheel traverse meansof two said grinding head units at different positions so that agrinding overlap zone produced when grinding said mill roll by said twogrinding head units is distributed in the roll axial direction.

Preferably, said grinding wheels of two said grinding head units arearranged with respective spindles inclined by a small angle in oppositedirections relative to the direction perpendicular to an axis of saidmill roll, so that respective contact lines between said abrasive layersand said mill roll are each defined only in one corresponding roll endside in the roll axial direction as viewed from the center of saidgrinding wheel.

To achieve the above second object, in accordance with the presentinvention, there is provided a rolling mill equipped with an on-lineroll grinding system, wherein said on-line roll grinding system furthercomprises displacement detector means for measuring a stroke of saidgrinding wheel in the roll axial direction given by said grinding wheeltraverse means, load detecting means for measuring the contact forcebetween said grinding wheel and said mill roll, and an on-line profilemeter including first profile calculating means for calculating aprofile of said mill roll from both the contact force measured by saidload detecting means and the stroke measured by said displacementdetector means under a condition of keeping a stroke of said grindingwheel movement means constant.

Also, to achieve the above second object, in accordance with the presentinvention, there is provided a rolling mill equipped with an on-lineroll grinding system, wherein said on-line roll grinding system furthercomprises first displacement detector means for measuring a stroke ofsaid grinding wheel movement means, second displacement detector meansfor measuring a stroke of said grinding wheel in the roll axialdirection given by sand grinding wheel traverse means, load detectingmeans for measuring the contact force between said grinding wheel andsaid mill roll, and an on-line profile meter including second profilecalculating means for calculating a profile Go said mill roll from boththe stroke measured by said first displacement detector means and thestroke measured by said second displacement detector means under acondition of keeping the contact force measured by said load detectingmeans constant.

In the above on-line roll grinding system, said on-line profile meterpreferably further includes means for calculating a deviation of aprofile of said mill roll measured by an off-line profile meter from theprofile of said mill roll determined by said first or second profilecalculating means, determining from said deviation an error inparallelism of the direction of movement of said grinding wheel by saidgrinding wheel traverse means with respect to said mill roll, andcompensating the roll profile determined by said first or second profilecalculating means based on the determined error in parallelism.

Preferably, said on-line profile meter further includes means forcalculating a deviation of the profile of said mill roll determined bysaid first or second profile calculating means from a preset target rollprofile, and controlling at least one of said grinding wheel movementmeans and said grinding wheel traverse means based on the calculateddeviation so that a grinding rate of said grinding wheel on said millroll is changed, for thereby grinding said mill roll to be identicalwith said target roll profile.

In this case, said control means preferably controls said grinding wheelmovement means to optionally change the contact force measured by saidload detecting means for thereby changing said grinding rate.

Alternatively, said control means may control said grinding wheelmovement means so that the contact force measured by said load detectingmeans is held constant and, simultaneously, controls said grinding wheeltraverse means to optionally change a traverse speed of said grindingwheel in the roll axial direction for thereby changing said grindingrate.

Also, said rolling mill preferably further comprises at least one ofroll bender means for applying bender forces to said mill roll, rollshift in a means for shifting said mill roll in the axial direction androll crossing means for making said pair of mill rolls crossed eachother, and control means for controlling at least one of the benderforces of said roll bender means, a shift position set by, said rollshifting means and a cross angle set by said roll crossing means basedon the profile of said mill roll measured by said first or secondprofile calculating means so that the strip crown approaches a targetstrip crown.

Further, in said rolling mill, said on-line roll grinding systempreferably further comprises control means for measuring an inclinationof the axis of said mill roll and controlling said grinding wheelmovement means and said grinding wheel traverse means so that saidgrinding wheel moves following a target roll profile in consideration ofthe inclination of the axis of said mill roll. In this case, preferably,said on-line roll grinding system further comprises presser means forfixing metal chocks supporting both ends of said mill roll, end holdingthe inclination of the axis of said mill roll constant during thegrinding.

In the above on-line roll grinding system, preferably, said grindingwheel, said grinding wheel drive means, said grinding wheel movementmeans and said grinding wheel traverse means constitute one grindinghead unit, and said on-line roll grinding system further comprises areference small-diameter zone formed on at least one end of said millroll and having a known diameter smaller than the diameter of a rollbarrel, and a displacement meter provided on said grinding head unit formeasuring a distance from said grinding head unit to said mill roll.

In the above rolling mill, preferably, said mill roll is a work roll,and said grinding wheel, said grinding wheel drive means, said grindingwheel movement means and said grinding wheel traverse means constitute agrinding head unit for grinding said work roll. Alternatively, sand millroll is a backup roll, and said grinding wheel, said grinding wheeldrive means, said grinding wheel movement means and said grinding wheeltraverse means constitute a grinding head unit for grinding said backuproll.

Preferably, said on-line roll grinding system further comprises areference small-diameter zone formed on at least one end of said millroll and having a known diameter smaller than the diameter of a rollbarrel, and roll diameter calculating means for pressing said grindingwheel against said mill roll at respective positions in said referencesmall-diameter zone and said roll barrel such that the contact forcebetween said grinding wheel and said mill roll has the same value,determining a periphery difference between said reference small-diameterzone and said roll barrel from a difference in displacement of saidgrinding wheel at that time, and determining a roll diameter in saidroll barrel from the determined periphery difference and the known rolldiameter in said reference small-diameter zone.

Furthermore, to achieve the above first and second objects, inaccordance with the present invention, there is provided a grindingwheel for an on-line roll grinding system comprising a plain wheel andan abrasive layer fixed to one side of said plain wheel and formed ofsuper abrasives, said plain wheel having an elastically deformingfunction to absorb vibration transmitted from a mill roll.

Operation of the present invention thus constructed is as follows.

First, in the present invention, with an elastically deforming functionimparted to the plain wheel as a part of the plain type grinding wheel,when the grinding wheel is pushed upon vibration of the mill roll, theplain wheel is deflected to momentarily absorb the vibration transmittedfrom the mill roll. Accordingly, fluctuations in the contact forcebetween the abrasive layer and the mill roll are held down within asmall range of the elastic force fluctuating upon the deflection of theplain wheel, thereby eliminating the occurrence of chattering marks.Further, an elastically deforming function is imparted to the plainwheel serving as a base for supporting the abrasive layer so that theabrasive layer is integral with a member having the elasticallydeforming function. Therefore, only both the abrasive layer and theplain wheel provide the mass forced to move upon the vibration from themill roll, whereby the movable mass can be very small and the naturalfrequency of the grinding wheel can be raised. Consequently, thevibrating mill roll can be correctly ground for a long period of timewithout causing any chattering marks due to resonance.

With the grinding wheel arranged such that the contact line between theabrasive layer and the mill roll is defined only in one side as viewedfrom the center of the grinding wheel, the plain wheel is allowed todeflect in cantilever fashion when pressed against the mill roll,whereby the elastically deforming function of the plain wheel iseffectively developed to easily absorb the vibration transmitted fromthe mill roll. Further, since the contact line is defined in only oneside of the wheel center, the occurrence of chattering marks isprevented and contact force control (described later) can be performedproperly.

With the abrasive layers formed of super abrasive grains, particularly,cubic boron nitride abrasives or diamond abrasives, the grinding wheelhas a grinding ratio more than 100 times that of the grinding wheel madeof aluminum oxide (Al₂O₂) abrasives or silicon carbide (SiC) abrasives,resulting in that the grinding can be continued for a long period oftime with a small weight of the grinding wheel. Consequently, themovable mass of the grinding wheel is further reduced, which iseffective in preventing resonance during the grinding, reducing theexchange pitch of the grinding wheel, and improving productivity of therolling mill.

As to the spring constant of the plain wheel, if the spring constant istoo large, the chattering marks are caused, the grinding ratio islowered, and further the abrasive layer is soon worn away thoroughly.Also, if the spring constant of the plain wheel is too large, thecontact force between the abrasive layer and the mill roll is so largelyfluctuated as to impose a difficulty in controlling the grinding ratedue to the contact force. Through the studies conducted by theinventors, it has been found that by setting the spring constant of theplain wheel to be not larger than 1000 Kgf/mm, preferably 500 Kgf/mm, itis possible to prevent the abrasive layer from being soon worn awaythoroughly, and use the grinding wheel continuously for not less than 5days once exchanged.

On the contrary, if the spring constant is small, the contact forceimposed on the grinding wheel due to the vibration of the mill roll isless fluctuated. The grinding ratio is therefore raised, but sensitivityof detecting the contact force is lowered and accuracy of grindingcontrol and roll profile measurement both based on the contact force isdegraded. Also, the smaller spring constant of the plain wheel meansthat the plain wheel is thinner and the grinding wheel is deflected to alarger extent with the same contact force, causing cracks in the plainwheel even with the contact force necessary for the grinding. Throughthe studies conducted by the inventors, it has been found that bysetting the spring constant of the plain wheel to be not less than 30Kgf/mm, the plain wheel can be prevented from cracking, and by settingthe spring constant to be not less than 50 Kgf/mm, even loadfluctuations generated with a periphery difference of 10 μm can bedetected.

As to compositions of the abrasive layer, in order to keep the grindingability constant and stabilize the grinding roughness without dressingin on-line roll grinding, it is required for the super abrasive grainsof the abrasive layer to be spontaneously edged at a constant rate.Proper spontaneous edging of the super abrasive grains needs adjustmentof the load imposed on one super abrasive grain. Through the studiesconducted by the inventors, it has been found that by setting density,i.e., concentration, of the super abrasive grains contained in theabrasive layer within the range of 50 to 100 and using a resin bond as abinder, the super abrasive grains are easily spontaneously edged, theservice life of the abrasive layer is not shortened, and hencecontinuous grinding is enabled without dressing. It has been also foundthat the size of the super abrasive grains, i.e., the grain size, isrequired to be in the range of 80 to 180 for obtaining the surfaceroughness of the mill roll in the range of 0.3 to 1.5 μm in average.

By continuously measuring the contact force between the mill roll andthe grinding wheel and then changing the contact force, the grindingrate of the grinding wheel on the mill roll per unit time is changed.Thus, by measuring the contact force at all times and controlling theposition of the grinding wheel by the grinding wheel movement means sothat the contact force is held constant, the mill roll can be ground bythe same dimension all over its cylindrical barrel. In other words, itis possible to grind the enter length of the mill roll while maintainingits original profile.

Also, by controlling the contact force in such a manner as to increasedand decrease, the mill roll can be ground into an arbitrary rollprofile. Further, by optionally controlling the traverse speed of thegrinding wheel in the roll axial direction while controlling the contactforce to be kept constant, the mill roll can also be ground into anarbitrary roll profile.

Unless the grinding wheel movement means for pressing the grinding wheelagainst the mill roll is constituted by using a mechanism having a highspring constant, there may cause chattering marks. As grinding wheelmovement means which is compact and has a high spring constant, optimumone is a mechanism in which a backlashes pre-loaded ball screw is drivenby an electric motor. This mechanism is also able to hold the positionof the grinding wheel constant during the grinding and to finely movethe grinding wheel back and forth.

When the grinding wheel is moved in the roll axial direction forgrinding the mill roll, it is required to grind the unrolling zone to alarger extent than the rolling zone for eliminating a peripherydifference between the unrolling zone and the rolling zone. Theunrolling zone exists at each of both ends of the mill roll. In view ofthat, a plurality of grinding head units each including the grindingwheel, the grinding wheel drive means, the grinding Wheel movement meansand the grinding wheel traverse means are disposed to be movableindependently of each other. Normally, two units are moved to remain inthe respective unrolling zones at both roll ends for grinding them. Onceper several times, the grinding head units are moved to the rolling zoneof the mill roll for grinding a fatigue layer on the surface therein.Thus, corresponding to wear of the rolling zone caused by rolling astrip, the unrolling zones are ground by the grinding wheel so that theroll profile free from a periphery difference can be maintained.

When a plurality of grinding head units are arranged to be movableindependently of each other for grinding a mill roll, there occurs anoverlap zone on the mill roll where the roll surfaces ground by adjacentgrinding wheels overlap with each other. The grinding Wheel traversemeans are stopped at different positions so that the overlap zone willnot always produce at the same position, thereby distributing theoverlap position.

As mentioned above, by making the contact line between the grindingwheel and the mill roll defined at one point, it is possible to carryout satisfactory grinding under constant conditions. In the presentinvention, therefore, the spindle of the grinding wheel is inclined by asmall angle relative to a line perpendicular to the axis of the millroll. By so arranging, in the on-line roll grinding system having aplurality of grinding wheels, there mays occur an interference betweenthe end of the grinding wheel and a housing if the spindles are inclinedin the same direction at both ends of the mill roll. Such aninterference in the grinding can be avoided by arranging the spindles ofthe grinding head units positioned at both ends of the mill roll to beinclined in opposite directions.

Accordingly, the grinding wheels can be freely moved to the respectiveends of the mill roll, and there is no need of particularly consideringthe dimension between the roll end and the housing.

Further, in the on-line profile meter having the first profilecalculating means of the present invention, the grinding wheel ispressed by the grinding wheel movement means against the rotating millroll to deflect the plain wheel in a certain amount, following which thegrinding wheel movement means is stopped and the contact force betweenthe mill roll and the grinding wheel at that time is measured by theload detecting means. Then, while moving the grinding wheel by thegrinding wheel traverse means in the axial direction of the mill roll,the stroke (axial position) of the grinding wheel is measured by thedisplacement detector means and the contact force is measured by theload detecting means.

Since the abrasive layer of the grinding wheel is supported by the plainwheel having an elastically deforming function and the plain wheel has afixed spring constant, the larger contact force increases a deflectionof the plain wheel. Conversely, the smaller contact force reduces adeflection of the plain wheel. On the other hand, if the axis of themill roll and the on-line roll grinding system or the grinding headunits are parallel to each other, the plain wheel of the grinding wheelis deflected to a larger extent with a larger diameter of the mill rolland to a smaller extent with a smaller diameter of the mill roll oncondition that the grinding wheel movement means is kept fixed.

In the first profile calculating means, therefore, the deflection of theplain wheel is determined from the value (contact force) measured by theload detecting means and processed to be correspondent to respectivepositions in the roll axial direction, thereby obtaining a profile ofthe mill roll.

Moreover, in the on-line profile meter having the second profilecalculating means of the present invention, the grinding wheel ispressed by the grinding wheel movement means against the rotating millroll to deflect the plain wheel in a certain amount, and then thegrinding wheel movement means is controlled so that the deflection ofthe plain wheel (i.e., the contact force) is always held constant. Whilemeasuring the stroke of the grinding wheel in the axial direction of itsspindle by the first displacement detector means, the grinding wheel ismoved in the roll axial direction by the grinding wheel traverse meansand the stroke (axial position) of the grinding wheel is measured by thesecond displacement detector means. Thus, in the second profilecalculating means, the stroke of the grinding wheel in the axialdirection of its spindle is determined from the measured value of thefirst displacement detector means and processed to be correspondent torespective positions in the roll axial direction, thereby obtaining aprofile of the mill roll.

The on-line roll grinding system is initially installed such that thedirection of traverse movement along the roll axial direction is inparallel to the axis of the mill roll. But, there is a fear in hotrolling mills that parallelism between them may change for a long periodof time due to the heat of strips. Unless such a change in parallelismis compensated, the roll profile measured as mentioned above cannot besaid as a true profile. The compensation means provided in the on-lineprofile meter compensates the error in parallelism and enables the moreprecise profile measurement.

More specifically, a mill roll is ground by an off-line roll grinderinstalled in a roll shop, and its roll profile after the grinding ismeasured by an off-line roll profile meter. After assembling the millroll into the rolling mill, a profile of the mill roll is measured byusing the first or second profile calculating means of the on-line rollprofile meter. Then, a deviation (difference) between both the profilevalues measured by the off-line and on-line roll profile meters isdetermined and, from this determined deviation, an error in parallelismof the on-line roll grinding system or the grinding head units withrespect to the roll axial direction is determined. Since then, at thetime of measuring a profile of the mill roll by using the first orsecond profile calculating means, the above error in parallelism issubtracted from the measured values obtained as mentioned above, therebycompensating the measured values to determine the correct measuredvalues.

In the control means for grinding the mill roll to be identical with atarget roll profile, after determining a profile of the mill roll by thefirst or second profile calculating means, a deviation of the determinedprofile of the mill roll from a preset target roll profile iscalculated. The grinding wheel movement means is controlled such thatthe grinding wheel is pressed against the mill roll by a stronger forcein the roll radial direction (at the roll axial position) in which theabove deviation is large, thereby controlling the grinding rate on themill roll so that the mill roll is ground into the target roll profile.Alternatively, while controlling the contact force between the mill rolland the grinding wheel to be held constant, the traverse speed of thegrinding wheel in the roll axial direction may be changed to vary thegrinding rate on the mill roll. In this case, too, the mill roll isground into the target roll profile.

After determining a profile of the mill roll by the first or secondprofile calculating means, the determined data is input to a systemcomputer for controlling the entire rolling mill and, based on the inputdata, roll benders provided in the rolling mill is operated to applybending forces to the mill rolls, thereby improving the profile of a hotstrip. When the rolling mill has roll shifting means for shifting themill roll in the axial direction or roll crossing means for making themill rolls crossed each other, the profile of a hot strip may beimproved by controlling such means. By so using the measured rollprofile as control data for the roll benders, the roll shifting means orthe roll crossing means, high-accurate strip crown control is enabled.

By moving the grinding head unit in the roll axial direction whilekeeping the distance between the axis of the mill roll and the distalend surface of the abrasive layer constant, the mill roll is ground tohave the same diameter over its entire length. By moving the grindinghead unit in such a manner as to optionally change the distance betweenthe axis of the mill roll and the distal end surface of the abrasivelayer, the contact force between the mill roll and the grinding wheel isincreased at the position providing the shorter distance where the millroll is ground to a larger extent. On the contrary, the contact forcebetween the mill roll and the grinding wheel is decreased at theposition providing the longer distance where the mill roll is ground toa smaller extent. Thus, for optionally creating and maintaining aprofile of the mill roll, the grinding wheel movement means is moved tocontrol the distance between the axis of the mill roll and the distalend surface of the abrasive layer such that the distal end surface ofthe abrasive layer draws the same path as the target roll profile of themill roll.

By measuring an inclination of the axis of the mill roll and grindingthe mill roll while controlling the grinding wheel movement means andthe grinding wheel traverse means such that the distal end surface ofthe abrasive layer moves along the target roll profile of the mill rollin consideration of the inclination, even if the axis of the mill rollis inclined, the correct roll profile compensated for the inclinationcan be always maintained.

When the work rolls is continuously ground for a long period of time,there may occur a difference in diameter between the upper and lowerrolls, i.e., a diameter difference. If such a diameter difference isincreased, values of rolling torque necessary for the upper and lowerrolls become so different as to impose undue forces on the spindles andso forth, which may result in a trouble. To prevent such a trouble, thesystem is usually controlled so that the diameter difference is keptwithin 0.2 mm/diameter.

By forming a reference small-diameter zone having a known roll diameterin at least one end of the mill roll, and measuring a peripherydifference between the reference small-diameter zone and the roll barrelby a displacement meter, the correct roll diameter can be alwaysdetermined. By making such measurement on the upper and lower rolls, thediameter reference can be monitored on-line.

Also, by measuring the roll diameter at both ends of the mill roll,whether the mill roll is tapered or not in the roll axial directionafter the grinding (i.e., cylindricity) can be confirmed.

Further, by pressing the grinding wheel against the mill roll atrespective positions in the reference small-diameter zone and the rollbarrel zone so that the contact force between the grinding wheel and themill roll has the same value, and determining a periphery differencebetween the reference small-diameter zone and the roll barrel from thedifference between two strokes of the grinding wheel measured at therespective positions at that time, the roll diameter can be measuredwithout using any displacement meter.

In hot rolling mills, while work rolls are worn away due to contact withhot strips, backup rolls supporting the work rolls also develop afatigue layer on their roll surfaces because the backup rolls arecontacted with the work rolls under high contact forces. By providingthe on-line roll grinding system on each of the backup rolls as well,the fatigue layer on the backup roll surfaces can be easily removed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view, partially sectioned, of principal parts of arolling mill equipped with an on-line roll grinding system according toa first embodiment of the present invention.

FIG. 2 is a sectional view; partially cut away, taken along line II—IIin FIG. 1.

FIG. 3 is a transverse sectional view of a roll grinding unit.

FIG. 4 is a vertical sectional view of the roll grinding unit.

FIG. 5 is a representation showing arrangement and structure of agrinding wheel and for explaining a vibration absorbing action of thegrinding wheel.

FIG. 6 is a representation showing the relationship in arrangementbetween the grinding wheels of the two roll grinding units.

FIG. 7 is a diagram for explaining a control system of the roll grindingunit.

FIG. 8 is a representation showing scratches produced on the surface ofa work roll by chattering.

FIG. 9 is a representation showing a sectional configuration of the workroll shown in FIG. 8.

FIG. 10 is a representation showing another example of arrangement ofthe grinding wheel and for explaining a vibration absorbing action ofthe grinding wheel.

FIG. 11 is a graph showing the relationship between the spring constantof a plain wheel of the grinding wheel and a grinding ratio.

FIG. 12 is a representation showing interference between the grindingwheel and a stand in the case of grinding the work roll under acondition that a spindle of the grinding wheel is inclined relative to aline perpendicular to the roll axis.

FIG. 13 is a graph showing the relationship of a contact force betweenthe work roll and the grinding wheel versus a grinding rate.

FIG. 14(A) is a representation showing an overlap zone of the grindingoccurred when using a plurality of grinding wheels, and FIGS. 14(B) and14(C) are representations for explaining a control method fordistributing the grinding overlap zone.

FIG. 15 is a diagram for explaining the overlap dispersion control.

FIG. 16 is a flowchart showing procedures of the overlap zonedistributing control.

FIG. 17 is a representation for explaining the positional relationshipbetween the work roll, a grinding wheel movement device, and adeflection of the grinding wheel in the case of measuring a rollprofile.

FIG. 18 is a flowchart for explaining a first roll profile calculatingfunction.

FIG. 19 is a flowchart for explaining a second roll profile calculatingfunction.

FIG. 20 is a flowchart showing procedures of compensating the rollprofile obtained by the first or second roll profile calculatingfunction based on roll profile data obtained off-line.

FIG. 21 is a flowchart showing procedures of grinding the work roll intoa target profile based on the roll profile obtained by the first orsecond roll profile calculating function.

FIG. 22 is a plan view, partially sectioned, of principal parts of arolling mill equipped with an on-line roll grinding system according toa second embodiment of the present invention.

FIG. 23 is a flowchart showing grinding control in the secondembodiment.

FIG. 24 is a flowchart showing rolling control according to a thirdembodiment of the present invention.

FIG. 25 is a transverse sectional view of principal parts of a rollingmill equipped with an on-line roll grinding system according to a fourthembodiment of the present invention.

FIG. 26 is a diagram showing the relationship between the work roll areference small-diameter zone, and a displacement of a measuring rod inthe fourth embodiment.

FIG. 27 is a representation for explaining a method of measuring aperiphery difference and a method of measuring cylindricity in thefourth embodiment.

FIG. 28 is a representation for explaining a method of measuring a wearof abrasives in the fourth embodiment.

FIG. 29 is a representation for explaining a method of measuring rolleccentricity in the fourth embodiment.

FIG. 30 is a representation for explaining the method of measuring awear of abrasives in the fourth embodiment.

FIG. 31 is a representation for explaining a method of measuring aperiphery difference in a rolling mill equipped with an on-line rollgrinding system according to a fifth embodiment of the presentinvention.

FIG. 32 is a flowchart showing procedures for practicing the method ofmeasuring a periphery difference in the fifth embodiment.

FIG. 33 is a side view, partially sectioned, of principal parts of arolling mill equipped with an on-line roll grinding system according toa sixth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be describedhereinafter with reference to the drawings.

First Embodiment At the outset, a description will be given of a firstembodiment of the present invention by referring to FIGS. 1 to 21.

In FIGS. 1 and 2, a rolling mill of this embodiment is of a 4 highrolling mill comprising a pair of rolls (upper and lower work rolls) 1a, 1 a for rolling a strip S, a pair of rolls (upper and lower backuprolls) 1 b, 1 b for respectively supporting the work rolls 1 a, 1 a, anda pair of roll benders 30, 30 for respectively allowing the work rolls 1a, 1 a to deflect. The work rolls 1 a, 1 a are supported by metal chocks3, 3 which are assembled into respective stands 4 on the operating anddrive sides. An entry guide is disposed on the entry side of the rollingmill for guiding the strip S to the work rolls 1 a. There are alsoprovided coolant headers 15, 15 for cooling heat of the work rolls 1 a,1 a generated during the rolling.

Such a rolling mill is equipped with an on-line roll grinding system ofthis embodiment. The on-line roll grinding system comprises two uppergrinding head units 5 a, 5 b (hereinafter represented by “5” in thedescription common to 1 a and 5 b) for the lower work roll 1 a and twolower grinding head units 6 a, 6 b (hereinafter similarly represented by“6” with only one of them being shown in FIG. 1) for the upper work roll1 a.

The upper grinding head units 5 a, 5 b are disposed corresponding to theoperating and drive sides of the work roll 1 a, respectively, and can beoperated to grind the workroll independently of each other. Likewise,the lower grinding head units 6 a, 6 b are disposed corresponding to theoperating and drive sides of the work roll 1 a, respectively, and can beoperated to grind the work roll independently of each other. These units5 a, 5 b and 6 a, 6 b each comprise, as shown in FIGS. 3 and 4, a plaintype grinding wheel 20 for grinding the work roll 1 a, a grinding wheeldrive device 22 for rotating the grinding wheel 20 through a spindle 21,a grinding wheel movement device 23 for pressing the grinding wheel 20against the work roll 1 a, and a grinding wheel traverse device 24 formoving the grinding wheel 20 in the axial direction of the work roll 1a.

As shown in FIG. 5 in an enlarged scale, the grinding wheel 20 comprisesa plain wheel 52 having a boss 52 a and an annular abrasive layer 51fixed to the surface of the plain wheel 52 on the side opposite to theboss 52 a, the plain wheel 52 being attached to the spindle 21. Also,the plain wheel 52 has an elastically deforming function to absorbvibration from the work roll, and is structured such that its deflectionis changed depending on the contact force between the work roll 1 a andthe abrasive layer 51. For the purpose of developing the elasticallydeforming function, the plain wheel 52 preferably has a spring constantof 1000 Kgf/mm to 30 Kgf/mm, more preferably 500 Kgf/mm to 50 Kgf/mm.The abrasive layer 51 is attached integrally with the plain wheel 52 byan adhesive so that it can be stably brought into close contact with thevibrating work roll 1 a.

The abrasive layer 51 is formed of super abrasive grains such as cubicboron nitride (generally called CBN) abrasives or diamond abrasives. Theabrasive grains have a concentration in the range of 50 to 100 and agrain size of in the rage of 80 to 180. The abrasive grains areaggregated together by using a resin bond as a binder. Material of theplain wheel 52 is of aluminum or an aluminum alloy for the purpose ofeasily radiating the grinding heat from the abrasive grains of theabrasive layer 51 and reducing movable mass of the grinding wheel 20.

As shown in FIG. 5, the grinding wheel 20 is arranged such that an axisGc1 of the spindle 21 is inclined by a small angle of α relative to aline Sc perpendicular to an axis Rc of the work roll 1 a, and a contactline between the abrasive layer 51 and the work roll 1 a is defined onlyin one side as viewed from the center of the grinding wheel. The angleof inclination a is preferably on the order of 0.5° to 1.0°. Such anarrangement of the grinding wheel 20 makes it possible to effectivelydevelop the elastically deforming function of the plain wheel 52, and toproperly control the contact force between the grinding wheel and thework roll (as described later).

Also, the grinding wheel 20 of the grinding head unit 5 a and thegrinding wheel 20 of the grinding head unit 5 b are arranged, as shownin FIG. 6, such that respective axes Gcl of their spindles 21 areinclined by the small angle of α in opposite directions relative torespective lines Sc perpendicular to the axis Rc of the work roll 1 a,and respective contact lines between the abrasive layers 51 and the workroll 1 a are each defined only in one corresponding roll end side asviewed from the center of the grinding wheel. Such an arrangementequally applies to the grinding wheel 20 of the grinding head unit 6 aand the grinding wheel 20 of the grinding head unit 6 b. This enablesthe grinding to be carried out to the opposite ends of the work roll 1 awithout interfering with the stands (as described later).

The grinding wheel drive device 22 comprises, as shown in FIG. 3, aliquid motor 54 (which may be instead of an electric motor) for drivingthe grinding wheel 20 to rotate at a predetermined circumferentialspeed, and a pulley shaft 54 b and a belt 55 for transmitting rotationof an output shaft 54 a of the liquid motor 54 to the spindle 21, theoutput shaft 54 a and the pulley shaft 54 b being coupled with eachother through parallel splines 54 c. The pulley shaft 54 b is rotatablysupported by a body 59. The spindle 21 is supported in the body 59through a pair of slide radial bearings 21 a, 21 b in a rotatable andaxially movable manner. On the side of the spindle 21 opposite to thegrinding wheel 20, a load cell 53 is accommodated in the body 59 formeasuring the contact force between the grinding wheel 20 and the workroll 1 a.

The body 59 is housed in a case 25 and the liquid motor 54 is attachedto the case 25. As shown in FIG. 4, the body 59 is mounted onto thebottom of the case 25 through a slide bearing 25 a to be movable in theaxial direction of the spindle 21.

The grinding wheel movement device 23 comprises, as shown in FIG. 3, amovement motor 57 attached to the case 25, a backlashless pre-loadedball screw 56 for moving the body 59 upon rotation of the movement motor57 in the direction toward or away from the work roll 1 a to therebyshift the grinding wheel 20, the spindle 21 and the load cell 53together back and forth, and an encoder 57 a for detecting an anglethrough which the movement motor 57 is rotated. The pre-loaded ballscrew 56 may be replaced by a backlashless gear mechanism.

The grinding wheel traverse device 24 comprises, as shown in FIG. 4, atraverse motor 58 attached to the case 25, a pinion 58 a fitted over arotary shaft of the traverse motor 58 and held in mesh with a rack 14,two pairs of guide rollers 26 attached to an upper surface of the case25 and engaging an upper or lower traverse rail 7, 8, and an encoder 58b for detecting the number of revolutions of the traverse motor 58. Asshown in FIGS. 1 and 2, the traverse rails 7, 8 are extended on theentry side of the work rolls 1 a, 1 a in parallel to the axes of thework rolls, and the rack 14 is formed on the side of the traverse rail 7or 8 opposite to the work roll. Thus, the grinding head units 5, 6 areeach smoothly movable in the axial direction of the work roll uponrotation of the traverse motor 58 through meshing between the pinion 58a and the rack 14, while being supported by the traverse rail 7, 8 viathe guide rollers 26.

The grinding head units 5, 6 are each required to not interfere with themetal chocks 3 when the corresponding work roll 1 a is exchanged.Therefore, the upper traverse rail 7 is slidably supported at its bothends on guides 9 attached to the stand 4, so that the grinding headunits 5 a, 5 b are moved rearwardly along with the traverse rail 8through a cylinder 11 and the guides 9. Also, the lower traverse rail 8is supported at its both ends by entry side guides 10 so that thegrinding head unit 6 is moved rearwardly along with the correspondingentry side guide 10 upon operation of a drive device (not shown).

In each of the grinding head units 5, 6, as shown in FIG. 7, themovement motor 57 of the grinding wheel movement device 23, and thetraverse motor 58 of the grinding wheel traverse device 24 arecontrolled by control units 13 a, 13 b, respectively. Also, detectedsignals from the load cell 53, the encoder 57 a of the grinding wheelmovement device 23, and the encoder 58 b of the grinding wheel traversedevice 24 are transmitted to a computer 13 c and then processed. Thecomputer 13 c has various processing functions and transmits signalsresulted from the processing to the control units 13 a, 13 b forcontrolling the movement motor 57 and the traverse motor 58. Theprocessing functions of the computer 13 c will be described later.

Operation and control of the on-line roll grinding system of thisembodiment will now be described.

A description will first be given of basic operation of the on-line rollgrinding system of this embodiment.

The work roll 1 a is rotated while vibrating at a frequency of 10 to 150c/s depending on the rolling speed. When a roll grinder having acylindrical grinding stone, which has been conventional in off-linegrinding systems, is employed in on-line grinding systems, thecylindrical grinding stone and the work roll contact with each otherthrough abrasives on the stone surface so that the work roll is groundby mutual collision of the metal on the roll surface and the abrasives.

Stated otherwise, the work roll is ground at the time the abrasives comeinto contact with the metal on the roll surface, but the grinding stonedeparts away from the work roll at a next moment, causing the abrasivesto rotate while beating the air. With such discontinuous grinding, thereoccurs chattering to render the roll surface and the roll sectionirregular as shown in FIGS. 8 and 9, respectively.

If a grinding wheel or stone is vibrated at the same frequency of thework roll, no changes are caused in the contact force between thegrinding wheel and the work roll. Because of the work roll vibrating ata high frequency of 150 c/s, however, it is difficult to make thegrinding wheel, including its entire frame, follow the work roll, i.e.,to vibrate the former in tune with the latter. In view of the above, ifthe grinding wheel itself is given with an elastically deformingfunction to absorb the vibration through deflection thereof, rather thanescaping the vibration through the grinding wheel and its entire frame,the movable mass is so reduced as to smoothly follow the vibration ofthe work roll, whereby fluctuations in the contact force between thegrinding wheel and the work roll become small.

In this embodiment, such an elastically deforming function is impartedto the grinding wheel itself by causing the plain wheel 52 as a part ofthe grinding wheel 20 to have an elastically deforming function. Morespecifically, the grinding wheel 20 is deflected by being pressedagainst the rotating work roll 1 a, while it is being rotated at acircumferential speed of 1000 m/min to 1600 m/inin of the abrasive layer51 measured at its outer periphery. During the grinding, the work roll 1a is vibrating back and forth, as explained above. The grinding wheel 20is pushed by this vibration, but at this time the plain wheel 52 isdeflected, as shown in FIG. 5, to momentarily absorb the vibrationtransmitted from the work roll 1 a. Accordingly, fluctuations in thecontact force between the abrasive layer 51 and the work roll 1 a areheld down within a small range of the elastic force fluctuating upon thedeflection of the plain wheel 52, thereby eliminating the occurrence ofchattering marks.

In addition, for a cylindrical grinding stone, it is difficult to givethe grinding stone itself with an elastically deforming function becausethe work roll and a spindle of the grinding stone are arranged inparallel to each other. For a plain grinding wheel, however, anelastically deforming function can be easily imparted to the grindingwheel itself because the work roll and the spindle of the grinding wheelare arranged in substantially orthogonal relation. For this reason,using a plain grinding wheel is more effective to grind the vibratingwork roll.

Thus, in this embodiment, an elastically deforming function is impartedto the plain wheel 52 as a base of the abrasive layer 51. Also, toeffectively develop the elastically deforming function, the grindingwheel 20 is arranged such that the contact line between the abrasivelayer 51 and the work roll 1 a is defined only in one side as viewedfrom the center of the grinding wheel, as shown in FIG. 5. Thisarrangement allows the plain wheel 52 to deflect in cantilever fashionwhen pressed against the work roll 1 a, thereby absorbing the vibrationtransmitted from the work roll 1 a.

For enabling the plain wheel 52 to deflect, a grinding wheel 20A may bearranged such that its spindle 21 has an axis offset from the axis ofthe work roll 1 a, as shown in FIG. 10. Furthermore, because of theabrasive layer 51 being annular in shape, even when the grinding wheel20 is pressed against the work roll 1 a in parallel thereto, thegrinding wheel contacts the work roll at two points of the abrasivelayer 51 on both sides of the wheel center and the plain wheel 52 candeflect. In this case, however, since the plain wheel 52 is supported attwo opposite ends, it is less deflected. By contacting the plain wheel52 with the work roll at one point as with this embodiment, a largerdeflection can be obtained by using a plain wheel of the same diameter.

A grinding wheel has an allowable range of the contact force between thework roll and the grinding wheel depending on the grinding ability ofabrasives. In the case of imparting an elastically deforming function tothe grinding wheel itself, the following condition must be satisfied inorder that the contact force is properly held in the allowable range andthe grinding wheel will not resonate even under vibration of the workroll.

F≧K×Amax

where

F: allowable range of the contact force

Amax: one-side amplitude of vibration of work roll

K: spring constant of elastic body (plain wheel)

Thus,

K≦F/Amax

Therefore, if an elastic body of the grinding wheel itself has a springconstant smaller than the above spring constant K determined from theallowable range F of the contact force between the grinding wheel andthe work roll and the one-side amplitude Amax of vibration of the workroll, the grinding wheel can grind the work roll while following thelatter at all times.

On the other hand, if the natural frequency of the grinding wheelcoincides with the vibration frequency of the work roll, the grindingwheel is caused to resonate and hence can no longer grind the work rollprecisely. For this reason, the natural frequency of the grinding wheelis preferably set to be as far as possible from the vibration frequencyof the work roll.

Fn>Frmax

where

Fn: natural frequency of the grinding wheel

Frmax: maximum number of vibration frequency of the work roll

Meanwhile, the natural frequency of the grinding wheel is expressed by:${Fn} = {\frac{1}{2\pi}\sqrt{K/M}}$

where

M: mass of the grinding wheel including the elastic body (i.e., movablemass)

Accordingly, in an attempt to raise the natural frequency of thegrinding wheel, it is required to increase the spring constant K of theelastic body, or reduce the mass M of the grinding wheel including theelastic body. But, as mentioned above, the spring constant K of theelastic body cannot be set larger than a certain value (F/Amax). Toraise the natural frequency of the grinding wheel, therefore, the massof the grinding wheel including the elastic body must be reduced.

On condition of F=4 Kgf and Mmax=30 μm, for example, K=133 Kgf/mm isresulted. Assuming that there hold Frmax=150 c/s and Fn=400 c/s,therefore, the movable mass M including the grinding wheel must be helddown to 0.2 Kg.

For the grinding wheel made of abrasive grains of aluminum oxide (Al₂O₂)or silicon carbide (SiC) which are generally used in grinding wheels orstones, if the movable mass is held down to 0.2 Kg, the grinding wheelis soon worn away thoroughly and must be exchanged may times per day.This greatly lessens the effect of grinding the work roll in the rollingmill, i.e., on-line.

To solve that problem, it is needed to use a grinding wheel with a highgrinding ratio (the volume of the work reduced/the volume of thegrinding wheel reduced).

When the grinding wheel is made of abrasive grains of aluminum oxide(Al₂O₂) or silicon carbide (SiC) which are generally used at thepresent, it is difficult to increase the grinding ratio more than 3 inthe case of grinding a hard work roll. In contrast, the grinding wheel20 of this embodiment, which is made of surer abrasive grains such ascubic boron nitride (generally called CBN) abrasives or diamondabrasives, has a grinding ratio above 300 even in grinding the work roll1 a, and hence exhibits a grinding ratio more than 100 times that of thegrinding wheel made of aluminum oxide (Al₂O₂) abrasives or siliconcarbide (SiC) abrasives. By employing the above super abrasive grains inthe grinding wheel of the on-line roll grinding system so as toadvantageously utilize such a high grinding ratio of the super abrasivegrains, the grinding can be continued for a long period of time with asmall weight of the grinding wheel.

Further, in this embodiment, the abrasive layer 51 is attached to thebase in the form of the plain wheel 52, and an elastically deformingfunction is imparted to the plain wheel 52, so that the abrasive layer51 is integral with a member having the elastically deforming function.Therefore, only both the abrasive layer 51 and the plain wheel 52provide the mass forced to move upon the vibration from the work roll 1a. Consequently, the movable mass can be very small and the naturalfrequency of the grinding wheel 20 can be raised.

As mentioned above, with this embodiment, the abrasive layer 52 isformed of super abrasive grains having a high grinding ratio (whichenable the grinding wheel to have a light weight and a long servicelife) for achieving the small movable mass, and the grinding wheel 20made integral with the plain wheel 52 having a proper spring constant ispressed against work roll 1 a while it is rotating. As a result, it ispossible to correctly grind the vibrating work roll for a long period oftime without causing chattering marks due to resonance.

A proper spring constant of the plain wheel 52 will now be described byreferring to experimental data plotted in FIG. 11. FIG. 11 showsexperimental data on the relationship between a spring constant of theplain wheel 52 and a grinding ratio. The experimental data was obtainedon condition that the circumferential speed of the work roll 1 a isvr=300 m/min, the circumferential speed of the grinding wheel is vg=1570m/min, the speed of movement of the grinding wheel in the roll axialdirection (i.e., the traverse speed) is vs=10 mm/sec, the vibrationfrequency of the work roll 1 a is f=35 Hz, and the one-side amplitude ofvibration of the work roll 1 a is a=0.01 mm.

As seen from FIG. 11, the grinding ratio lowers with the larger springconstant, and rises with the smaller spring constant. In other words, ifthe spring constant is too large, the chattering marks are caused, thegrinding ratio is lowered, and further the abrasive layer 51 is soonworn away thoroughly. In order to minimize the exchange pitch of thegrinding wheel 20 and avoid a reduction in productivity due to exchangeof the grinding wheel, each grinding wheel is required to permitcontinuous grinding for not less than 5 days once exchanged. Meetingthis exchange pitch generally needs a grinding ratio not less than 50,preferably 250. Since the grinding wheel 20 made of super abrasivegrains is expensive, the grinding ratio must be as high as possible forthe purpose of reducing the production cost. The reason why the grindingratio lowers with the larger spring constant of the plain wheel 52 isthat the contact force imposed on the grinding wheel 20 due to thevibration of the work roll 1 a is fluctuated to a larger extent and,therefore, a larger force acts or the abrasive grains of the abrasivelayer 51 correspondingly to make those abrasive grains fall offtherefrom. Also, if the spring constant of the plain wheel 52 is toolarge, the vibration of the work roll 1 a cannot be fully absorbed bythe grinding wheel 20 and the resulting load is transmitted to the loadcell 53, which results in larger fluctuations in the measure value ofthe contact force and hence a difficulty in controlling a grinding ratebased on the contact force between the work roll 1 a and the abrasivelayer 51 (as described later).

On the contrary, if the spring constant is small, the contact forceimposed on the grinding wheel 20 due to the vibration of the work roll 1a is less fluctuated. The grinding ratio is therefore raised, butaccuracy of grinding control and roll profile measurement (describedlater) both based on the contact force is degraded. The reason why theaccuracy of grinding control and roll profile measurement is degraded isthat the force acting on the spindle 21 upon deflection of the grindingwheel 20 becomes so small that the load cell 53 cannot detect change inthe load corresponding to small irregularities.

Assuming the spring constant of the plain wheel 52 to be 50 Kgf/mm, forexample, the load difference produced by a periphery difference of 10 μmis ΔF=50×0.01=0.5 (Kgf) which is almost a limit of the detectable range,judging from resolution of general load cells. Also, the smaller springconstant of the plain wheel 52 means that the plain wheel 52 is thinnerand the grinding wheel 20 is deflected to a larger extent with the samecontact force, causing undue forces in the abrasive layer 51 due todistortion. Thus, if the spring constant is smaller than 30 Kgf/mm,there would occur cracks in and peel-off of the abrasive layer 51 fromthe plain wheel 52 even with the contact force necessary for thegrinding.

It has been found from the foregoing data that the spring constant ofthe plain wheel 52 is preferably in the range of 1000 Kgf/mm to 30Kgf/mm, more preferably 500 Kgf/mm to 50 Kgf/mm.

Compositions of the abrasive layer 51 will now be described. When thegrinding wheel 20 employs the abrasive layer 51 made of super abrasivegrains, the abrasive layer 51 is usually subjected to dressing inoff-line roll grinding to keep the grinding ability constant andstabilize the grinding roughness. In on-line roll grinding, however,there is a difficulty in dressing the abrasive layer 51 from thestandpoints of space and so forth. In order to keep the grinding abilityconstant and stabilize the grinding roughness without dressing inon-line roll grinding, it is required for the super abrasive grains ofthe abrasive layer 51 to be spontaneously edged at a constant rate.Proper spontaneous edging of the super abrasive grains needs adjustmentof the load imposed on one super abrasive grain. For this purpose, it isrequired to set density, i.e., concentration, of the super abrasivegrains contained in the abrasive layer 51 within the range of 50 to 100,and use a resin bond as a binder which is worn away along with the superabrasive grains while holding them together. If the concentration is notless than 100, the spontaneous edging of the super abrasive grains wouldbe hard to occur, resulting in a decrease of the grinding ability. Ifthe concentration is not larger than 50, the service life of the superabrasive grains would be shortened. Further, if a pitolifido bond or thelike which is hard to wear away is used as a binder, projection of thesuper abrasive grains from the binder surface would be so small as torequire dressing. With a combination of the above range of concentrationand the binder comprising a resin bond, the super abrasive grains can beeasily spontaneously edged to enable the continuous grinding withoutdressing. It has been also found that the size of the super abrasivegrains, i.e., the grain size, is required to be in the range of 80 to180 for obtaining the surface roughness of the work roll 1 a in therange of 0. 3 to 1.5 μm in average.

Operation depending on an arrangement of the grinding wheel 20 now bedescribed. As mentioned above, the grinding wheel 20 is arranged suchthat the axis Gc1 of the spindle 21 is inclined by the small angle of αrelative to the line Sc perpendicular to the axis Rc of the work roll 1a, and the contact line between the abrasive layer 51 and the work roll1 a is defined only in one side as viewed from the center of thegrinding wheel. With such an arrangement of the grinding wheel 20, theplain wheel 52 can effectively develop its elastically deformingfunction, also as mentioned above. Further, because of the abrasivessurface 51 being annular, if the surface of the abrasive layer 51 ispressed against the work roll 1 a in parallel relation, there aredefined contact lines between the abrasive layer 51 and the work roll 1a at two points on both sides of the wheel center. As a result of thetwo contact lines being defined, the work roll 1 a is simultaneouslyground at those two points. Therefore, if the work roll 1 a has aperiphery difference, the two grinding surfaces interfere with eachother to cause chattering marks. Also, the contact at two points betweenthe grinding wheel and the work roll leads to a difficulty incontrolling the contact force therebetween. In this embodiment, sincethe contact line between the annular abrasive layer 51 and the work roll1 a is defined only at one point on one side of the wheel center, thechattering is prevented to enable proper control of the contact force(as described later).

When the spindle 21 is inclined by the small angle of α relative to theline Sc perpendicular to the axis Rc of the work roll 1 a, there is afear that a zone not subjected to the grinding may occur at one end ofthe work roll 1 a, or the grinding wheel 20 may interfere with the stand4 on that one end side of the work roll 1 a, as shown in FIG. 12.Therefore, the grinding wheel 20 of the grinding head unit 5 a and thegrinding wheel 20 of the grinding head unit 5 b are arranged, as shownin FIG. 6, such that the respective axes Gc1 of their spindles 21 areinclined by the small angle of α in opposite directions relative to therespective lines Sc perpendicular to the axis Rc of the work roll 1 a,and the respective contact lines between the abrasive layers 51 and thework roll 1 a are each defined only in one corresponding roll end sideas viewed from the center of the grinding wheel. This arrangementenables the work roll 1 a to be ground over its entire length withoutcausing the above interference with the stand. The foregoing descriptionequally applies to the grinding wheel 20 of the grinding head unit 6 aand the grinding wheel 20 of the grinding head unit 6 b.

Control of the on-line roll grinding system of this embodiment will nowbe described. The on-line roll grinding system of this embodiment hasvarious control functions below:

(1) roll profile grinding control

(2) independent grinding control

(3) overlap zone distribution control

(4) roll profile measurement as a on-line roll profile meter

(5) roll profile compensation

(6) combination of roll profile measurement and roll profile grindingcontrol

These control functions are previously stored in the form of programs inthe computer 13 c.

(1) Roll Profile Grinding Control

A description will first be given of the roll profile grinding control.FIG. 13 shows experimental data on the relationship of a contact force Fbetween the abrasive layer 51 of the grinding wheel 20 and the work roll1 a versus a grinding rate Q per unit time. The experimental data wasobtained at the circumferential speed of the work roll 1 a of or=300m/min, 600 m/min and 900 m/min on condition that the circumferentialspeed of the grinding wheel is vg=1570 m/min, the speed of movement ofthe grinding wheel in the roll axial direction (i.e., the traversespeed) is vs=10 mm/sec, the vibration frequency of the work roll 1 a isf=35 Hz, and the one-side amplitude of vibration of the work roll 1 a isa=0.01 mm. As seen from the graph of FIG. 13, the grinding rate Q perunit time changes almost linearly depending on the contact force Fbetween the abrasive layer 51 and the work roll 1 a. Accordingly, thegrinding rate Q of the work roll 1 a can be optionally changed bycontrolling the contact force F between the abrasive layer 51 and thework roll 1 a by the grinding wheel movement device 23 disposed in eachof the grinding head units 5, 6.

To perform the above control, the load cell 53 is arranged in abutmentwith the end of the spindle 21 on the side opposite to the grindingwheel for more precisely detecting the contact force F in thisembodiment. Also, the relationship between the contact force F and thegrinding rate Q shown in FIG. 13 is previously stored in the computer 13c shown in FIG. 7, and the detected contact force F is input to thecomputer 13 c. Then, the deflection of the plain wheel 52 is changed bigthe movement motor 57 to reach the target grinding rate, therebycontrolling the contact force F (see FIG. 21). As a result, the workroll 1 a can be ground to a predetermined profile.

The grinding rate is also changed by varying the speed of movement ofthe abrasive layer 51 in the roll axial direction (i.e., the traversespeed) while keeping the contact force F between the abrasive layer 51and the work roll 1 a constant. In other words, when the abrasive layer51 is moved at a higher speed, the time during which the abrasives areheld in contact with the work roll is shortened and the grinding rate isreduced. Conversely, moving the abrasive layer 51 at a lower speedincreases the grinding rate. Accordingly, by controlling the traversespeed of the abrasive layer 51, the grinding rate of the work roll 1 acan also be changed optionally.

Specifically, the detected contact force F is input to the computer 13c, the traverse speed of the abrasive layer 51 is controlled by thetraverse motor 57 to reach the target grinding rate, while controllingthe deflection of the plain wheel 52 by the movement motor 57 so thatthe contact force F is kept constant (see FIG. 21). As a result, thework roll 1 a can be ground to a predetermined profile.

When controlling the contact force F between the abrasive layer 51 andthe work roll 1 a by the grinding wheel movement device 23, as mentionedabove, if there exists a backlash in the axial direction of the spindle21, the movable mass moving back and forth upon the vibration of thework roll 1 a is abruptly increased, whereby the. contact force Fbetween the abrasive layer 51 and the work roll 1 a is changed to alarge extent. If the contact force is changed so large, the grindingwheel movement device 23 can no longer control the contact force. Tomake such a backlash as small as possible, in this embodiment, thebacklashless pre-loaded ball screw 56 is used as the grinding wheelmovement device 23, and other slide parts are constituted by using thoseparts which have small clearances. Further, the movement moter 57 fordriving the ball screw 56 comprises an electric motor. As a result, thecontact force can be easily controlled by the grinding wheel movementdevice 23, making it possible to hold the position of the grinding wheel20 during the grinding and finely move the grinding wheel 20 back andforth.

(2) Independent Grinding Control

A description will now given of the independent grinding control of thegrinding head units 5 a, 5 b or 6 a, 6 b.

Because of contact with the strip, the rolling zone of the work roll 1 ais worn away about 2 μm/radius after the rolling of one coil, while theunrolling zone of the work roll is not worn away because of no contactwith the strip. Accordingly, there occurs a periphery difference betweenthe rolling zone and the unrolling zone. The unrolling zone exists atboth ends of the work roll on the operating and drive sides.

In the case of mounting the grinding head units 5 a, 5 b or 6 a, 6 btogether onto a single frame, when one grinding head unit 5 a or 6 a ispositioned in the unrolling zone on the operating side, the othergrinding head unit 5 b or 6 b is positioned at the center of the workroll 1 a. Therefore, in attempt to grind one unrolling zone by onegrinding head unit, the other grinding head unit is positioned in therolling zone and can not grind the other unrolling zone.

Also, when the two grinding head units are mounted together onto asingle frame, the frame has a length larger than half of the work roll 1a, causing a problem that a coolant ejected from the coolant headers 15during the rolling is blocked by the frame and the work roll 1 a cannotbe cooled sufficiently.

In this embodiment, the two grinding head units 5 a, 5 b or 6 a, 6 b arearranged for each work roll 1 a and are controlled to perform thegrinding independently of each other. Therefore, the two grinding headunits 5 a, 5 b or 6 a, 6 b are divided in their role such that theunrolling zone on the operating side can be ground mainly by thegrinding head unit 5 a or 6 a and the unrolling zone on the drive sidecan be ground mainly by the grinding head unit 5 b or 6 b. As a result,the unrolling zones subjected to no abrasion can be ground to a largerextent so that there occurs no periphery difference between the rollingzone and the unrolling zones. Such control is performed by rotating thetraverse moter 58 with a command from the control unit 13 b to move thegrinding head unit 5 or 6 over the traverse rail 7, 8 through meshingbetween the pinion 58 b and the rack 14, and by rotating the movementmoter 57 with a command from the control unit 13 a to advance theabrasive layer 51 through movement of the ball screw 56.

The grinding head unit 5 or 6 is sometimes moved to the center of thework roll 1 a for removing the roughed roll surface in the rolling zoneor the fatigue layer on the roll surface. This control is also performedby rotating the traverse moter 58 with a command from the control unit13 b to move the grinding head unit 5 or 6.

In that way, it is possible to efficiently grind the unrolling zones ofthe work roll 1 a at its both ends and hold the roll profile constantfor a long period of time. It is to be noted that when the work roll 1 ais long as encountered in rolling mills for slabs, the grinding headunits 5, 6 may be provided three or four such that the units are movedto respective zones to be ground for grinding those zones independentlyof one another.

Further, in this embodiment, since the grinding head units 5 a, 5 b or 6a, 6 b are separated from each other, the work roll 1 a can be cooledsufficiently by the coolant ejected from the coolant headers 15 duringthe rolling.

(3) Overlap Zone Distribution Control

A description will now be given of the distribution control for anoverlap zone which occurs by using the grinding control unit 5 or 6comprising plural units.

When the plural grinding head units 5 a, 5 b or 6 a, 6 b are moved tothe center of the work roll 1 a, the grinding surfaces of the grindingwheels 20 a, 20 b adjacent to each other mutually overlap at the centerof the work roll 1 a, as shown in FIG. 14(A). At this time, if thegrinding surfaces always overlap at the same position Ta, the overlapzone is ground to a larger extent than the remaining zone, resulting ina grinding error in the overlap zone.

If a plurality of grinding head units are mounted together onto a singleframe, a plurality of corresponding grinding wheels are always moved inthe same stroke as one-piece and, therefore, the grinding overlap zoneinevitably occurs at the same position. Thus, an grinding error cannotbe avoided in the overlap zone, with a fear of producing a peripherydifference on the roll surface.

In this embodiment, by operating the two grinding head units 5 a, 5 b or6 a, 6 b independently of each other, the grinding overlap zone of thegrinding wheels 20 a, 20 b does not remain at one location as indicatedby the overlap line Ta, but can be distributed over the range betweenoverlap lines Tb and Tc spanning in the roll axial direction, as shownin FIGS. 14(B) and 14(C). Consequently, the grinding error in theoverlap zone can be reduced.

FIGS. 15 and 16 show procedures of the above control for distributingthe overlap zone. These control procedures are previously stored in theform of programs in the computer 13 c. First, the grinding head unit 5 ais operated to start grinding from the operating side end of the workroll 1 a toward the roll center (step 100), the grinding being continuedup to a position closer to the drive side by a distance L1 from the rollcenter Rm (step 101). Then, the direction of movement of the grindinghead unit 5 a is reversed for grinding the work roll 1 a up to theoperating side end (step 102). In parallel, the other grinding head unit5 b is operated to start grinding from the drive side end of the workroll 1 a toward the roll center (step 103), the grinding being continuedup to the position closer to the drive side by the distance L1 from theroll center Rm (step 104). Then, the direction of movement of thegrinding head unit 5 a is reversed for grinding the work roll 1 a up toa position closer to the operating side by a distance L2 from the rollcenter Rm (step 105) and, in parallel, the direction of movement of thegrinding head unit 5 b is also reversed for grinding the work roll 1 aup to the drive side end (step 106). Subsequently, the direction ofmovement of the grinding head unit 5 a is reversed again for grindingthe work roll 1 a a up to the operating side end (step 107) and, inparallel, the direction of movement of the grinding head unit 5 b isreversed again for grinding the work roll 1 a up to the position closerto the operating side by the distance L2 from the roll center Rm (step108). Then, after changing values of L1, L2, the above procedures arerepeated (steps 109 and 110). In that way, the work roll 1 a can beground while distributing the overlap zone.

(4) Roll Profile Measurement as On-line Roll Profile Meter

A description will now be given of operation of the on-line roll profilemeter built in the on-line roll grinding system.

In the system of this embodiment in which the plain wheel 52 of thegrinding wheel 20 has an elastically deforming function and the contactforce between the work roll 1 a and the abrasive layer 51 is controlledby the movement moter 57 of she grinding wheel movement device 23, therelationship between the roll profile, the position of the grindingwheel movement device, ant the contact force is expressed below byreferring to a schematic representation of FIG. 17.

Z(x)=S(x)−F(x)/K

where

x: coordinate in the roll axial direction

Z(x): roll profile (mm)

S(x): position of the grinding wheel movement device (mm)

F(x): contact force between the work roll and the grinding wheel (Kgf)

K: spring constant of the grinding wheel (Kgf/mm)

First, assuming that the grinding head unit is traversed in the axialdirection of the work roll 1 a while keeping the grinding wheel movementdevice 23 fixed, since the S(x) is always constant, change in the rolldiameter is expressed by:

ΔZ(x)=−ΔF(x)/K

Thus, the quotient resulted by dividing the change ΔF(x) in the contactforce between the work roll and the grinding wheel by the springconstant K is a deflection of the grinding wheel 20, i.e., the changeΔZ(x) in position of the roll surface, and the roll profile is obtainedby processing that position change to be correspondent to the roll axialcoordinate. This is a first roll profile calculating function.

FIG. 18 shows processing procedures for the first roll profilecalculating function. These processing procedures are previously storedin the form of programs in the computer 13 c. First, the grinding wheel20 of the grinding head unit 5 a is pressed against the operating sideend of the work roll 1 a and the grinding wheel movement device is fixedin place (step 200). Then, while keeping the grinding wheel movementdevice fixed, the traverse motor 58 is rotated to move the grinding headunit 5 a in the roll axial direction (step 201). During this movement,change in the contact force between the work roll 1 a and the abrasivelayer 51 is measured by the load cell 53 (step 202), and the deflectionof the grinding wheel 20 is calculated from the aforesaid relationship(step 203). At the same time, the position of the grinding head unit 5 ain the roll axial direction is measured based on a signal from theencoder 58 b of the traverse moter 58 (step 204). Then, a roll profileis calculated from both the roll axial position of the grinding headunit 5 a and the deflection of the grinding Wheel 20 (step 205). For thegrinding head unit 5 b, the similar procedures to the above steps areexecuted to calculate a roll profile (step 206). However, the grindinghead unit 5 b is moved from the drive side end in the roll axialdirection. The roll profiles obtained from movement of the two grindinghead units 5 a, 5 b are combined with each other to determine a profileover the entire length of the work roll 1 a (step 207).

As another method of measuring the roll profile, change ΔS(x) in theposition of the grinding wheel movement device is detected whilecontrolling the grinding wheel movement device so that the contact forceF(x) between the work roll and the grinding wheel is always kept at aconstant load in the roll axial direction.

Since F(x)/K is constant in the roll axial direction, change in the rolldiameter is expressed by:

ΔZ(x)=ΔS(x)

Thus, the roll profile is obtained by determining the change ΔS(x) inthe position of the grinding wheel movement device from the detectedvalue of the encoder 57a of the movement moter 57, and processing thatposition change to be made correspondent to the roll axial coordinate.This is a second roll profile calculating function.

FIG. 19 shows processing procedures for the second roll profilecalculating function. These processing procedures are previously storedin the form of programs in the computer 13 c. First, the grinding wheel20 of the grinding head unit 5 a is pressed against the operating sideend of the work roll 1 a (step 300). Then, and the grinding wheelmovement device is fixed in place (step 200). Then, after tentativelysetting the grinding wheel movement device to a certain position, thetraverse moter 58 is rotated to move the grinding head unit 5 a in theroll axial direction (step 301). During this movement, change in thecontact force between the work roll 1 a and the abrasive layer 51 ismeasured by the load cell 53, and the position (stroke position) of thegrinding wheel movement device is controlled by the movement moter 57 sothat the measured contact force is kept constant (step 302). Adisplacement of the grinding wheel 20 is calculated based on a signalfrom the encoder 57 a of the movement moter 57 (step 303). At the sametime, the position of the grinding head unit 5 a in the roll axialdirection is measured based on a signal from the encoder 58 b of thetraverse moter 58 (step 304). Then, a roll profile is calculated fromboth the roll axial position of the grinding head unit 5 a and thedisplacement of the grinding wheel 20 (step 305). For the grinding headunit 5 b, the similar procedures to the above steps are executed tocalculate a roll profile (step 306). However, the grinding head unit 5 bis moved from the drive side end in the roll axial direction. The rollprofiles obtained from movement of the two grinding head units 5 a, 5 bare combined with each other to determine a profile over the entirelength of the work roll 1 a (step 307). In that way, the profile of thework roll can be measured on-line by using the equipment of the on-linegrinding system.

(5) Roll Profile Compensation

A description will now be given of a function of compensating the rollprofile by using the measured value of the on-line roll profile meter.

Although the traverse rails 7, 8 of the on-line roll grinding system areinitially installed in parallel to the axis of the work roll 1 a, thereis a fear in hot rolling mills that parallelism between them may changefor a long period of time due to the heat of strips. Unless such achange in parallelism is compensated, the work roll profile measured asmentioned above cannot be said as a true profile. The computer 13 cexecutes this compensation following the procedures shown in FIG. 20.

First, the work roll 1 a is ground by an off-line roll grinder installedin a roll shop, and its roll profile after the grinding is measured byan off-line roll profile meter in advance. The measured roll profile isinput to the computer 13 c (step 400). After assembling the work roll 1a ground by the off-line roll grinder into the rolling mill, a profileof the work roll 1 a is measured by using the above-mentioned first orsecond profile calculating function of the on-line roll profile meter(step 401). Then, a difference between both the roll profiles measuredby the off-line and on-line roll profile meters is determined (step402). The determined difference is recognized as a deformation (error inparallelism) of the traverse rail for the grinding head units and storedin the computer 13 c (step 403). Then, after grinding the work roll 1 aon-line in the subsequent rolling, a profile of the work roll 1 a ismeasured by using the first or second profile calculating function (step404). The measured roll profile values are compensated by subtractingthe above error in parallelism therefrom (step 405), and the resultingcorrect measured values are stored in the computer 13 c (step 406). As aresult, the precise profile of the work roll 1 a can be determined.

(6) Combination of Roll Profile Measurement and Roll Profile GrindingControl

A description will now be given of a function of grinding the work roll1 a into a target roll profile with the above-explained grinding controlmethod by using the thus obtained profile data of the work roll, withreference to FIG. 21. The processing procedures shown in FIG. 21 arealso previously stored in the computer 13 c.

First, a target roll profile is input in the computer 13 c beforehand(step 500). Then, a profile of the work roll 1 a is measured by usingthe first or second profile calculating function (step 501). At thistime, the above process for compensating the roll profile using themeasured values of the off-line roll profile meter is executed, ifnecessary. After determining the correct profile of the work roll 1 a, adifference between the determined profile of the work roll and thetarget roll profile is determined (step 502). From the determineddifferences at respective axial roll positions, the amounts to be groundat these respective positions are calculated (step 503), and thengrinding conditions at the respective axial roll positions arecalculated (step 504). In the case of carrying out the grinding controlwhile changing the contact force, the contact force between the workroll 1 a and the abrasive layer 51 is controlled by the movement moter57 of the grinding wheel movement device based on the relationship ofthe contact force F between the work roll 1 a and the abrasive layer 51versus the grinding rate, whereby the work roll grinding rate is changedso as to grind the work roll 1 a into the target profile (step 505). Inthe case of carrying out the grinding control while changing thetraverse speed, the traverse speed of the grinding wheel 20 iscontrolled by the traverse motor 58 of the grinding wheel traversedevice 24, whereby the work roll grinding rate is changed so as to grindthe work roll 1 a into the target profile (step 505).

In that way, the work roll 1 a is provided with a profile identical tothe target roll profile.

Second Embodiment

A second embodiment of the present invention will be described withreference to FIGS. 22 and 23. In these figures, those members which areidentical to those in FIGS. 1 to 7 are denoted by the same referencenumerals.

During continued use of hot rolling mills, as abrasion of the stands 4and the metal chocks 3 progresses under an influence of the coolant andso on, the axis Ra of the work roll 1 a Which has been initiallyperpendicular to the strip S may incline as indicated by Rb in FIG. 22.In this embodiment, the target roll profile is maintained orcompensated, taking into account such a inclination of the work roll 1a.

FIG. 23 is a flowchart showing control procedures of this embodiment.These control procedures are previously stored in the form of programsin the computer 13 c (see FIG. 7).

First, to determine an inclination of the axis of the work roll 1 a, thegrinding head units 5 a, 5 b are respectively moved to the roll ends onthe operating and drive sides (step 600). On each of the operating anddrive sides, the movement moter 57 is rotated to press the abrasivelayer 51 of the grinding wheel 20 against the work roll 1 a (step 601).When the grinding wheel 20 is pressed until the load cell 53 detects apredetermined load, a displacement of the grinding wheel from thereference position at that time is measured by the encoder 57 a built inthe movement moter 57 (step 602). The load at Which a displacement ofthe grinding wheel is measured is set to the same value on both theoperating and drive sides.

Then, a difference in displacement of the grinding wheel 20 between theoperating and drive sides is calculated (step 603), and thisdisplacement difference is divided by the distance between measuringpoints on the operating and drive sides to determine an inclination ofthe axis of the work roll 1 a, the determined inclination being storedin the computer 13 c (step 604).

Subsequently, a stroke position of the grinding wheel 20 required forobtaining the target profile is calculated by the above-mentioned methodprior to grinding the work roll 1 a. The calculated stroke position iscompensated by using the above stored inclination of the axis of thework roll 1 a (step 606), and the number of revolutions of the grindingmovement moter 57 is controlled so that the distance from the axis ofthe work roll 1 a to the leading end of the abrasive layer 51 is heldconstant (step 607).

By so performing control, even with the work roll 1 a inclined, thedistance between the roll axis and the abrasive layer 51 can be heldconstant to enable constant position grinding. With this constantposition grinding, if there is a periphery difference between therolling zone and the unrolling zones as shown in FIG. 2, the deflectionof the plain wheel 52 is large in the unrolling zones and small in therolling zone corresponding to the smaller roll diameter. Such adeflection difference produces a difference in the contact force betweenthe abrasive layer 51 and the work roll 1 a, and the contact forcedifference in turn produces a difference in the grinding ability. Thus,the unrolling zones is ground to a larger extent than the rolling zoneso that the periphery difference between the rolling zone and theunrolling zones gradually reduced and disappeared. In that way, even ifthe axis of the work roll 1 a is inclined, the roll profile of the samediameter can be obtained.

In the above constant position grinding, if the axis of the work roll 1a is displaced during the rolling, there occurs an error in the profilegrinding. To prevent such an error, as shown in FIG. 22, a chock presser31 is mounted to a bender block 30 a for each of roll benders 30, 30 forthereby horizontally pressing the metal chock 3 against a bender block30 a on the opposite side. The chock presser 31 may be mounted to themetal chock 3 rather than the bender block 30 a. The chock presser 31comprises a piston 32 and a liquid pressure chamber 33. The piston 32 ispushed under a liquid pressure supplied to the liquid pressure chamber33, whereupon the metal chock 3 is brought into abutment by a force ofthe piston 32 with the bender block 30 a on the opposite side. Byproviding the chock presser 31 on each of both the metal chocks 3, 3,the axis of the work roll 1 a is held fixed, making it possible to grindthe work roll 1 a into the target profile without being affected byabrasion of the stands 4 and the metal chocks 3, etc.

In the case of applying an arbitrary roll profile to the work roll 1 a,the work roll 1 a is ground by an off-line roll grinder into such anarbitrary roll profile and this roll profile is previously stored as atarget roll profile in the computer 13 c (see FIG. 7). After that, thenumber of revolutions of the grinding wheel movement moter 57 iscontrolled so as to move the grinding wheel 20 following the rollprofile, thereby carrying out position control grinding. Even though therolling zone of the work roll 1 a is worn away to render the rollprofile changed, the original nal roll profile can be correctlymaintained through compensate grinding at all times because the grindingwheel 20 is moved following the correct roll profile. Also in this case,an inclination of the axis of the work roll 1 a is compensated in a likemanner to the above. Specifically, an inclination of the axis of thework roll 1 a is determined from displacements of the grinding wheels 20on the operating and drive sides and, taking into account thisinclination, the number of revolutions of the grinding wheel movementmoter 57 is controlled so as to move the grinding wheel 20 following thetarget roll profile. As a result, even if the axis of the work roll 1 ais inclined, the work roll 1 a can have the correct and constant rollprofile for a long period of time.

Additionally, if the inclination of the axis of the work roll 1 adetermined from displacements of the grinding wheels 20 is in excess ofa certain allowable value, this may lead to a zigzag motion or the likeof the strip S. Therefore, the computer 13 c may issue an alarm in suchan event.

Third Embodiment

A third embodiment of the present invention will be described withreference to FIG. 24. This embodiment is intended to perform strip crowncontrol based on the measured roll profile values.

While the work roll 1 a is assembled into the stands 4 after beingground by an off-line grinder, it produces a thermal crown by the heatof the strip S during the rolling of the strip S. Conventionally, such athermal crown is calculated by a process computer (not shown), and theroll benders 30 provided in the rolling mill are controlled based on thecalculated amount of thermal crown for causing the work roll 1 a tobend, so that the strip crown of the strip S approaches a target value.However, the thermal crown calculated by the process computer is oftendifferent from the actual thermal crown depending on conditions.

To prevent such a drawback, this embodiment carries out strip crowncontrol according to procedures as shown in FIG. 24. First, a rollprofile is measured by using the above-mentioned first or second rollprofile calculating function (step 700). This measurement is performedin accordance with programs previously stored in the computer 13 c (seeFIG. 7), as explained before. Then, taking into account the measuredroll profile, a host computer calculates an optimum bender force foreach of the roll benders 30 from the target strip crown and the targetstrip shape (step 701). The bender forces of the roll benders 30 arecontrolled in accordance with the calculated result, causing the workroll 1 a to bend (step 702), followed by rolling the work roll 1 a underthat state (step 703). As a result, the crown of the strip S can becloser to the target value.

Though not shown, for a rolling mill equipped with a roll shiftingdevice for shifting the work roll in the axial direction, the crown ofthe strip S can be still closer to the target value by controlling notonly the bender forces, but also an axial shift position of the workroll. For a rolling mill equipped with a roll crossing device for makingthe pair of work rolls 1 a, 1 a crossed to each horizontally, the crownof the strip S can be ever closer to the target value by controllingboth the bender forces and the cross angle. Of course, by inputtingprofile values determined by the roll profile measurement after thegrinding to the process computer and then performing the above shapecontrol process, the strip crown is further improved over the entirestrip length.

Fourth Embodiment

A fourth embodiment of the present invention will be described withreference to FIGS. 25 to 30. In these figures, those members which areidentical to those in FIGS. 1 to 7 are denoted by the same referencenumerals.

When the work rolls 1 a is continuously ground for a long period of timein the on-line roll grinding system, an error in the grinding rate maybe so accumulated as to cause a difference in roll diameter between theupper and lower work rolls, i.e., a diameter difference. Generally, ifsuch a diameter difference becomes larger than 0.2 mm/diameter, adifference in rolling torque between the upper and lower work rollsexceeds an allowable value and, if it continues to increase, roll drivespindles and so forth may be damaged. To prevent such a trouble, it isrequired to measure diameters of the upper and lower work rolls afterthe grinding at a certain time interval. In this embodiment, a systemfor measuring diameters of the work rolls on-line after the grinding isadded to the above-explained on-line roll grinding system.

In FIG. 25, the work roll 1 a is formed on at least one end thereof witha reference small-diameter zone 39 a which has been ground and measuredby an off-line grinder so as to have a smaller diameter than that of astrip passage zone (i.e., a roll barrel). The roll diameter in thereference small-diameter zone 39 a is assumed to be D1, as shown in FIG.26. Also, a roll periphery difference measuring device 40 is integrallyattached to the case 25 of the grinding head unit 5. The grinding headunit 6 also has the same construction.

The roll periphery difference measuring device 40 comprises a measuringrod 41 integral with a piston 41 a, and a case 42 for guiding both thepiston 41 a and the measuring rod 41. The case 42 is attached to a cover47 in turn attached to the body 59 so that the case 42 is movabletogether with the grinding wheel 20. Within the case 42, there isdefined a liquid pressure chamber 46 for pushing both the piston 41 aand the measuring rod 41 toward the work roll 1 a, and there aredisposed a displacement meter 43 for measuring a displacement of themeasuring rod 41 and a spring 44 for discharging a liquid pressure outof the liquid pressure chamber 46 and returning the measuring rod 41back to its home position at the time other than measurement.

A description will now be given of a method of measuring a diameter ofthe work roll by the roll periphery difference measuring device 40 withreference to FIG. 27. In FIG. 27, the grinding head unit 5 is moved inthe roll axial direction so that the measuring rod 41 takes a positionA, followed by stopping there. Then, at the position A, a liquidpressure is introduced to the liquid pressure chamber 46, causing themeasuring rod 41 to contact the reference small-diameter zone 39 a ofthe work roll 1 a. The position of the measuring rod 41 at that time ismeasured by the displacement meter 43. Subsequently, the grinding headunit 5 is moved to a position B, the measuring rod 41 is pressed againinto contact with the work roll 1 a, and the position of the measuringrod 41 at that time is measured by the displacement meter 43. Adifference between the values measured by the displacement meter 43 atthe positions A, B is calculated by the computer 13 c (see FIG. 7),thereby determining a roll periphery difference. Given the rollperiphery difference being x, the diameter D of the work roll 1 a isexpressed by D=D1+2x. More precisely, the diameter D of the work roll 1a is measured as follows. By making a half turn of the work roll 1 a,the periphery differences are measured at opposite sides angularlyspaced 180 degrees from each other, the measured values being assumed tobe x1, x2, respectively. In this case, the diameter D of the work roll 1a is expressed by D=D1+x1+x2. From the diameters of the upper and lowerwork rolls thus obtained, there can be determined a diameter differencetherebetween.

A description will now be given of a method of measuring cylindricity ofthe work roll 1 a using the roll periphery difference measuring device40.

As shown in FIG. 27, reference small-diameter zones 39 a, 39 b havingbeen subjected to measurement are formed at both ends of the work roll 1a. On the side of the reference small-diameter zone 39 a, thedisplacement of the measuring rod 31 is measured at each of thepositions A, B, as explained above, thereby determining a diameterdifference x between the reference small-diameter zone 39 a and the workroll 1 a. On the side of the reference small-diameter zone 39 b,likewise, another grinding head unit 5 is moved to measure thedisplacement of the measuring rod 31 at each of positions C, D, therebydetermining a diameter difference y between the reference small-diameterzone 39 b and the work roll 1 a. From these two diameter differences xand y, a deviation x−y therebetween is determined. This deviation of thediameter difference is divided by the distance between the two measuringpoints to obtain cylindricity. The cylindricity thus obtained can beused for compensating the inclination of the axis of the work roll 1 ain the above-mentioned measurement using the roll profile meter.

The roll periphery difference measuring device 40 can also be used tomeasure a wear of the abrasive layer 51 for indicating exchangeinformation of the abrasive layer 51. A method of measuring a wear ofthe abrasive layer 51 will now be described with reference to FIG. 28.

First, after attaching a fresh grinding wheel 20 to the rolling mill,the abrasive layer 51 is pressed by a grinding wheel movement deviceagainst the work roll 1 a under a predetermined force as indicated at aposition F. The distance from the grinding head unit 5 to the work roll1 a at that time is measured by the displacement meter 43 and stored inthe computer 13 c (see FIG. 7). After grinding the work roll for acertain period of time, the measurement is performed in a like manner tothe above as indicated at a position E, thereby obtaining the measuredvalue of the displacement meter 43. By determining a difference sbetween the previous measured value and the current measured value, theresulting difference s provides the amount by which the grinding wheel20 has been worn away during the period of time between the twomeasurements. Assuming that the abrasive layer 51 has a thickness t1 ofits abrasive portion, the remaining thickness t2 of the abrasive portionis expressed by t2=t1−s. Thus, the exchange information of the abrasivelayer 51 can be indicated based on the value of t2.

Then, after grinding the work roll 1 a, whether the work roll iseccentric or not can be measured by using the roll periphery differencemeasuring device 40. This method of measuring an eccentricity will nowbe described with reference to FIGS. 29 and 30.

The measuring rod 41 is pressed against the reference small-diameterzone 39 a of the work roll 1 a to measure a displacement of the workroll 1 a and, at the same time, the grinding wheel 20 is pressed againstthe work roll 1 a to measure a displacement of the work roll 1 a. If thework roll is not eccentric, there produces a displacement due to entirevibratory movement of the work roll, but the reference small-diameterzone 39 a and the zone which has been subjected to the grinding, i.e.,the roll barrel, are displaced similarly, meaning that the displacementmeasured by the displacement meter 43 becomes equal to the displacementdetermined from the load detected by the load cell 53 and the springconstant of the grinding wheel 20. However, if the work roll iseccentric, there produces a difference between the two measureddisplacements during one rotation of the work roll. This displacementdifference can be regarded as the eccentricity of the work roll.

Fifth Embodiment

A fifth embodiment of the present invention will be described withreference to FIGS. 31 to 32 and FIG. 7. This embodiment is intended tomeasure a diameter of the work roll 1 a without using any displacementmeter.

First, as shown in FIG. 31, a reference small-diameter zone 60 is formedat one end of the work roll 1 a beforehand. The reference small-diameterzone 60 can be formed by grinding one end of the work roll 1 a by anoff-line grinder so as to provide a diameter smaller x than the rolldiameter of the zone which will be ground by the on-line grinding system(i.e., the roll barrel). The process described so far is the same asthat in the above fourth embodiment. Then, a roll diameter D1 in thereference small-diameter zone 60 is measured and input to the computer13 c. The periphery difference x between the roll barrel and thereference small-diameter zone is preferably about 1 mm, though thisvalue depends on an inclination of the grinding wheel 20 with respect tothe work roll 1 a.

Then, control procedures shown in FIG. 32 are executed. These controlprocedures are previously stored in the form of programs in the computer13 c. First, rotation of the work roll 1 a and rotation of the grindingwheel 20 are both stopped to keep the reference small-diameter zone 60from being ground by the grinding wheel (steps 800) and (step 801). Thegrinding wheel 20 is traversed to a position X of the referencesmall-diameter zone 60 (step 802), and then the grinding wheel 20 ismoved by the grinding wheel movement device so as to contact the workroll 1 a. The grinding wheel 20 is further pressed against the work roll1 a until the contact force therebetween reaches a predetermined value(step 802). When the load cell 53 detects that the predetermined contactforce has been reached, the movement moter 57 is stopped, followingwhich the position of the grinding wheel at that time is detected by theencoder 57 a and stored (step 804).

Thereafter, it is determined whether the measurement has been made atboth the position X of the reference small-diameter zone 60 and aposition Y of the roll barrel (step 805). If not, then the grindingwheel 20 is traversed to the position Y of the roll barrel (step 806).At the position Y, as with the case of the reference small-diameter zone60, the grinding wheel 20 is pressed against the work roll 1 a until thecontact force therebetween reaches a predetermined value (step 803).When the predetermined contact force is reached, the position of thegrinding wheel 20 at that time is detected by the encoder 57 a andstored (step 804).

Subsequently, a difference between the stroke positions of the grindingwheel 20 measured at the positions A and B is calculated (step 807).This difference provides the periphery difference x. Finally, since theroll diameter D1 in the reference small-diameter zone 60 is known, aroll diameter Dn of the roll barrel is determined from the followingformula (step 808).

Dn=D 1+x

In that way, the diameter of the work roll 1 a after the grinding can beeasily determined and used for judging the timing of roll exchange orconfirming the difference in diameter between the upper and lower workrolls.

Sixth Embodiment

While the above description has been made in connection with on-linegrinding of the mill roll 1 a, i.e., the work roll, the rolling millalso includes the upper and lower backup rolls 1 b, 1 b contacting thework rolls, the surfaces of the backup rolls being also roughed andsubjected to formation of a fatigue layer. FIG. 33 shows an embodimentin which an on-line roll grinding system is provided on each of theupper and lower backup rolls 1 b, 1 b. The on-line roll grinding systemfor the backup roll basically has the same construction and functions asthose of the foregoing on-line roll grinding system for the work roll.By providing the on-line roll grinding systems for the backup rolls sothat the surfaces of the upper and lower backup rolls 1 b, 1 b areground on-line as with the surfaces of the work rolls 1 a, 1 a, it ispossible to prolong the exchange pitch of the upper and lower backuprolls 1 b, 1 b and improve productivity of hot rolling facilities.

SUMMARY OF ADVANTAGES

According to the present invention, as fully described above, since thevibration of each mill roll is absorbed by an elastically deformingfunction of the plain wheel of the grinding wheel, the mill roll can beprecisely ground with high surface roughness without causing anychattering marks and resonance.

Since the abrasive layer of the grinding wheel is formed of superabrasive grains, the movable mass of the grinding wheel can be reduced,which is more effective in preventing resonance. Also, the service lifeof the grinding wheel can be prolonged to grind the mill roll for alonger period of time while rolling a strip or the like. It is hencepossible to greatly reduce the exchange pitch and increase productivityof rolling facilities to a large extent.

Since the grinding rate of the grinding wheel per unit time is changedby varying the contact force between the mill roll and the grindingwheel, the mill roll can be ground into an optional roll profile.

Since the grinding wheel movement device is constituted by using a ballscrew mechanism or a gear mechanism which has a small backlash, thespring constant of the movement device is so increased as to preventchattering marks caused by the backlash of the movement device.

Since at least two grinding head units capable of grinding independentlyof each other are disposed for one mill roll, the roll profile free froma periphery difference can be maintained over the entire length of themill roll.

Since the grinding overlap zone produced on the mill roll by, using theplural grinding wheels is distributed, precision grinding is enabledwithout grinding errors.

Since the mill roll is ground by using units corresponding to both rollends and having their spindles which are inclined in oppositedirections, it is possible to grind the entire length of the mill rollwithout interfering with the stand.

Since the contact force between the mill roll and the grinding wheel isdetected for calculating a profile of the mill roll, the roll profilecan be measured while grinding the mill roll. By controlling the contactforce of the grinding wheel or the speed of movement of the grindingwheel in the roll axial direction based on the roll profile thusmeasured, the mill roll can be easily provided with a target profile.

Further, by simultaneously using an on-line roll grinding system and anon-line roll profile meter so that the roll profile optimum for rollingis maintained at all times, it is possible to realize completelyschedule-free rolling.

Since an error in parallelism between the direction of traverse movementof the grinding wheel and the mill roll is compensated, the more preciseprofile can be measured.

Since shape control means such as roll benders are controlled inaccordance with the roll profile determined by the on-line roll profilemeter, high-accurate strip crown control is enabled.

Since the grinding wheel grinds the mill roll while moving along thetarget roll profile, the profile of the mill roll can be optionallycreated and maintained. At this time, since an inclination of the axisof the mill roll is measured and the grinding wheel is caused to movealong the target roll profile for the grinding in consideration of suchan inclination of the roll axis, the correct roll profile can always bemaintained even if the roll axis is inclined.

Since the grinding is carried out under a condition that the metalchocks of the mill roll are pressed against the stands or the benderblocks, the correct roll profile can always be maintained without beingaffected by swear of the stands and the metal chocks.

Since the reference small-diameter zone is formed at the end of the millroll and a periphery difference between the reference small-diameterzone and the zone of the mill roll subjected to grinding i.e., the rollbarrel) is measured by a displacement meter or the grinding head unititself, it is possible to determine the correct roll diameter at alltimes and monitor a difference in diameter between the upper and lowerrolls on-line. It is also possible to confirm cylindricity of the millroll.

Finally, since the on-line roll grinding system is provided on thebackup roll, a fatigue layer on the surface of the backup roll can beeasily removed.

What is claimed is:
 1. A rolling mill equipped with an on-line rollgrinding system comprising: a pair of rotatable circular grinding wheelsspaced from one another in an axial direction of a mill roll forgrinding the mill roll; each grinding wheel being configured as aresilient elastic body which is elastically deflected during mill rollgrinding operations; said grinding wheels having respective spindlesarranged to incline in opposite directions relative to a directionperpendicular to an axis of the mill roll, said spindles of the grindingwheels being arranged offset vertically from the axis of the mill roll,and drive means for positively driving and rotating each of saidgrinding wheels.
 2. A rolling mill equipped with an on-line rollgrinding system comprising: a rotatable circular grinding wheel forgrinding a mill roll; said grinding wheel being configured as aresilient elastic body which is elastically deflected during mill rollgrinding operations; said grinding wheel having a spindle arranged toincline relative to a direction perpendicular to an axis of the millroll, and drive means for positively driving and rotating each of saidgrinding wheels.
 3. A rolling mill equipped with an on-line rollgrinding system comprising: a rotatable circular grinding wheelconfigured to function by itself as a resilient elastic body forgrinding a mill roll; said grinding wheel having a spindle arrangedoffset vertically from an axis of the mill roll; said grinding wheelbeing configured as a resilient elastic body which is elasticallydeflected during mill roll grinding operations, and drive means forpositively driving and rotating each of said grinding wheels.
 4. Arolling mill equipped with an on-line roll grinding system comprising: arail arranged to extend along in an axial direction of a mill roll; apair of rotatable circular grinding wheels arranged in the roll axialdirection over said rail for grinding the mill roll; each grinding wheelbeing configured as a resilient elastic body which is elasticallydeflected during mill roll grinding operations; said grinding wheelshaving respective spindles supported by said rail so as to incline inopposite directions relative to a direction perpendicular to an axis ofthe mill roll, and drive means for positively driving and rotating eachof said grinding wheels.
 5. A rolling mill equipped with an on-line rollgrinding system comprising: a rail arranged to extend along in an axialdirection of a mill roll; and a pair of rotatable circular grindingwheels arranged in the roll axial direction over said rail for grindingthe mill roll and each having a spring constant of 1000 Kgf/mm to 30Kgf/mm; said grinding wheels having respective spindles supported bysaid rail so as to incline in opposite directions relative to adirection perpendicular to an axis of the mill roll.
 6. A rolling methodin a rolling mill equipped with an on-line roll grinding systemcomprising: arranging a pair of rotatable circular grinding wheels in anaxial direction of a mill roll for grinding the same, said grindingwheels having respective spindles arranged to incline in oppositedirections relative to a direction perpendicular to an axis of the millroll, each grinding wheel being configured as a resilient elastic bodywhich is elastically deflected during mill roll grinding operations;said spindles of the grinding wheels being arranged offset verticallyfrom the axis of the mill roll; and rolling a strip while grinding themill roll by positively driving and rotating each of said grindingwheels with said grinding wheels being pressed thereagainst.
 7. Arolling method in a rolling mill equipped with an on-line roll grindingsystem comprising: arranging a rotatable circular grinding wheelconfigured to function by itself as a resilient elastic body forgrinding a mill roll, said grinding wheel having a spindle arrangedoffset vertically from an axis of the mill roll; and rolling a stripwhile grinding the mill roll by positively driving and rotating saidgrinding wheel with said grinding wheel being pressed thereagainst whilesaid grinding wheel is being bent.
 8. A rolling method in a rolling millequipped with an on-line roll grinding system comprising: arranging arotatable circular grinding wheel configured to function by itself as aresilient elastic body for grinding a mill roll, said grinding wheelhaving a spindle arranged to offset vertically from an axis of the millroll; and rolling a strip while grinding the mill roll by positivelydriving and rotating said grinding wheel with said grinding wheel beingpressed thereagainst while said grinding wheel being elastically bent.9. A rolling method in a rolling mill equipped with an on-line rollgrinding system comprising: arranging a rail to extend along in an axialdirection of a mill roll; arranging a pair of rotatable circulargrinding wheels spaced from one another in the roll axial direction oversaid rail for grinding the mill roll, said grinding wheels each beingconfigured to function by itself as a resilient elastic body, saidgrinding wheels having respective spindles supported by said rail so asto incline in opposite directions relative to a direction perpendicularto an axis of the mill roll; and moving said grinding wheels along saidrail in the roll axial direction with the grinding wheels being pressedthereagainst while being elastically bent thereby to roll a strip whilegrinding the mill roll.
 10. A rolling method in a rolling mill equippedwith an on-line roll grinding system comprising: arranging a rail toextend along in an axial direction of a mill roll; arranging a pair ofrotatable circular grinding wheels in the roll axial direction over saidrail for grinding the mill roll and each having a spring constant of1000 Kgf/mm to 30 Kgf/mm, said grinding wheels having respectivespindles supported by said rail so as to incline in opposite directionsrelative to a direction perpendicular to an axis of the mill roll; andmoving said grinding wheels along said rail in thee rail axial directionwith the grinding wheels being pressed thereagainst while being bentthereby to roll a strip while grinding the mill roll.